Answer: b.

Explanation:
We prefer something to something else, not than. However, we could say that we like something more than we like something else. This tends to be a tricky distinction for people learning English, which is not surprising. I am surprised, though, by how frequently prefer/than appears online. A quick look around, searching for prefer to or prefer than brought up these headlines:

• MPs prefer to sling mud than clean it up (from the Sydney Morning Herald)
• For Those Who Prefer to Text than Talk, College and Career Strategist Elizabeth Venturini Guides Them to Grace and Opportunity with Skills Beyond the Right Knife and Fork (from PRWeb)
• Why do people prefer comics digitally than physical print? (Yahoo! Answers q)

And that’s when I wasn’t specifically looking for prefer/than. I also came across this tweet response from an editor: “I prefer writing from scratch than overhauling an entire story myself.”

We could say “I prefer writing from scratch rather than overhauling an entire story myself.” But maybe throwing than into the mix that way leads to confusion, so let’s just stick with prefer/to and leave it at that.

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