How is written prose more complex than casual speech?

A. It expresses feelings and emotions.

B. It contains short thoughts and ideas.

C. It uses a more precise vocabulary.

D. It offers a chance for quick clarification.

C. It uses a more precise vocabulary.

Written prose is more complex than casual speech because:

C. It uses a more precise vocabulary.

Due to the possibility to revise the text and to think what is the best option in each case, the written prose is more complex than casual speech, that it is usually subject to improvisation.