Answer: c.
Explanation:
A lingua franca (also known as a working language, bridge language or vehicular language) is a third language that speakers of two different native tongues use to communicate. For example, before the 18th century, Latin was the lingua franca of Europe because most educated people learned it. Thus, people from various European countries could communicate without being able to speak each other’s native language.

A pidgin is a simplified language that speakers of two different languages develop to communicate.

A creole is a language that develops naturally from a combination of languages.

The first lingua franca was actually a language called Lingua Franca.

From Wikipedia:

The original Lingua Franca was a mixed language composed mostly (80%) of Italian with a broad vocabulary drawn from Turkish, French, Greek, Arabic, Portuguese and Spanish. It was in use throughout the eastern Mediterranean as the language of commerce and diplomacy in and around the Renaissance era. At that time, Italian speakers dominated seaborne commerce in the port cities of the Ottoman empire. Franca was the Italian word for Frankish. Its usage in the term lingua franca originated from its meaning in Arabic and Greek, dating from before the Crusades and during the Middle Ages, whereby all Western Europeans were called “Franks” or Faranji in Arabic and Phrankoi in Greek during the times of the late Eastern Roman Empire.^[3] The term lingua franca is first recorded in English in 1678.

Amanda Briney on About.com also has an interesting article on lingua franca.

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