Is the human use of spoken or written words as a communication system.
a. syntax. b. grammar c. language d. vocabulary

I believe the correct answer among the choices listed above is option C. Language is the human use of spoken or written words as a communication system. Across the globe, there are thousands of languages that is used by people to connect and communicate with each other.

The answer would be either your second choice (B) or the last one (D)