Answer: Either, depending on where you are.

Explanation:

In the U.S., roofs is the standard plural of roof; elsewhere rooves is fairly common but becoming less so. The same holds true for an increasing number of words ending in “f.”

The standard/traditional rule for words ending in “f”  – the one I grew up with, of course — is that we substitute a “v” for the “f” and add “es” to form the plural:

The rule on “roofs” has changed so completely in the U.S. that Merriam-Webster no longer even has an entry for “rooves.” Although the standard rule for most words ending in “f” still holds,  in casual speech and writing words like “calfs,” “elfs” and “loafs” are appearing more and more. What that means, in all likelihood, is that more will follow and the old rule will change, so that words ending in “f” just take an “s” for pluralization, like most words ending in a consonant.

And there’s nothing wrong with that, other than that in the transitional period, people who say “calfs,” “elfs” and “loafs” may be ridiculed by those of us clinging to the old rule. That being the case, stick to the standard for formal writing.

Writers on the Net provides resources on irregular plurals.

A tip of the editor’s visor to @Guy_in_PEI for the inspiration for this post. (What, no one’s wearing those green eyeshades any more? Oh, I AM behind the times.)

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Answer: a.

Explanation:
An ellipsis is a sequence of three dots used to indicate that something continues, or sometimes to indicate that something — like a thought — has trailed off. The plural of “ellipsis” is “ellipses.”

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Answer: c

Explanation:
“Money” as a mass noun is never incorrect and — in this case — the other two words are. They are often used, incorrectly, to refer to especially large sums of money, as if we need double pluralization to express such a large wad of dough. Like when “super” isn’t enough to describe the magnitude of something and you’ve got to call it “super-duper.”

Here’s HarwardCommunications blog, a writing guide for non-native speakers of English, on the issue:
“We would never say I found some monies under the bed / There are some monies under the bed. And it is incorrect to say I found a money under the bed.”

That being the case, it doesn’t make any more sense to refer to “monies available at the end of the fiscal quarter.”

However, in financial and business writing the other forms are standard language used to refer to discrete streams of funds, whether sources or targets. Examples include monies (that’s the common current spelling) earmarked for various corporate initiatives or monies due from various accounts.

Outside of that arena, stick with “money” and you won’t be wrong.

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Answer: a.

Explanation:
Mice is the clear winner in a Google poll:
Computer mice: 319,000
Computer mouses: 30,600
(But that’s not why we say it’s correct.)

There’s a lot of discussion about this issue online and, although consensus seems to be for mice, some folks insist that mouses is more correct or even mouse, like the plural of moose (which is moose). Here’s a sample argument:

MOUSE is an acronym, and is short for Manually-Operated User-Selection Equipment so technically MOUSE is already the plural (… Equipments?) Most people, however pluralise acronyms, and initials in general, by adding a small s, so it would be MOUSEs, which seems a bit silly. Mice is also wrong, as it doesn’t stand for anything, but it does make more grammatical sense than calling them MOUSE or MOUSEs. (NB: If a MOUSE was so called because it looked like the animal, then mice would be correct, but that isn’t the case, although small body, long tail, who knows…)

We’re not sure about that acronym story. It seems to us more likely a backronym, made up with likely words to stand for the letters in the name. Because, after all, everything should be an acronym, right? (OT: Did you know there’s a sarcasm mark? Maybe I’ll go see if I can’t round one up.)

The OED lists the plural as mouses. Much as we hate to disagree with the OED, we will do so in this case.

Why do we say with such certainty that the plural of (computer) mouse is mice? We went to the source. In this video, at about 10:03, Douglas Engelbart, who invented the mouse, refers to it in the plural as mice. Oh, and by the way? He said the name was chosen for the device’s resemblance to its furry namesake — yes, small body, the long tail.Maybe the tendency to scamper…

So there you have the authorative answer: Douglas Englebart says the plural of mouse is mice. So it would just be silly for us to say it should be something else. Especially mouses.

Thanks to @OnewordTF for the idea!

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Explanation:
By itself, majority is singular but if it’s linked to a group, as above, use the plural form.

The Economist has more information about collective nouns.

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Answer: b.

Explanation: Use the usual form for pluralizing a word ending in s, which is to add es. That’s the rule I chose to follow. However, there are those who argue for OSs. See a debate about this issue here.

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Explanation:
Criterion is singular; criteria is plural. However, Merriam-Webster notes that usage doesn’t always comply. And we know what happens when that situation hits the tipping point — when’s the last time you heard someone mention an agendum?

Here’s the entry:
Pronunciation: \krī-ˈtir-ē-ən also krə-\
Function: noun
Inflected Form(s): plural -ria \-ē-ə\ also cri·te·ri·ons
Etymology: Greek kritērion, from krinein to judge, decide
Date: 1622

1 : a standard on which a judgment or decision may be based
2 : a characterizing mark or trait
synonyms: see standard
usage The plural criteria has been used as a singular for over half a century . Many of our examples, like the two foregoing, are taken from speech. But singular criteria is not uncommon in edited prose, and its use both in speech and writing seems to be increasing. Only time will tell whether it will reach the unquestioned acceptability of agenda.

Here’s a little quiz on criteria/criterion.

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Answer: b

Explanation:
If you follow AP style, the only case that calls for an apostrophe to pluralize is that of individual letters, as in”Mind your P’s and Q’s,” for example.

Ryan’s linguistic blog lists this horrifying example of misuse found online:

“Hey guy’s. I was wondaring do you love dog’s or cat’s? I like dog’s!!! Please say dog’s. Dog’s rock!”

Well, at least s/he was consistent.

Explanation:
According to the AP Stylebook, the only case in which an apostrophe is used to create a plural form is that of individual letters.

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Answer: b

Explanation:
A request for proposal (RFP) is a single request, generally seeking multiple proposals. (The singular form is sometimes spelled request for proposals.) The plural form is requests for proposal because there are multiple requests. It’s like cups of tea (rather than cup of teas) or sets of tennis (rather than set of tennises).

So, if the plural is requests for proposal, what’s the plural of RFP?
Although request for proposal is pluralized as requests for proposal — which makes it seem like the plural should be RFP — we treat the abbreviation as a single word. So, to indicate multiple requests, make it RFPs.