A lingua franca may also be called:

A. A dead language

B. A borrowed language

C. A working language

D. An incomplete language

C. A working language

Explanation:

Lingua franca (no accent 'i ') is a Latin expression for contact language or language of relationship resulting from contact and communication between linguistically distinct groups or members of groups for international trade and other more extensive interactions.

In the Roman Empire and the following millennium the lingua franca was Greek in the east and Latin in the west.

Later, a lingua franca used in the 14th century (or even earlier) Mediterranean Sea region to this day was known to Mediterranean sailors, including the Portuguese.

English is the current lingua franca in the world of international business in the west and in diplomacy.

I think it may be B, a borrowed language. The others don't seem right.