Which of the following situations would summarizing be the most useful?
a. writing a persuasive essay
b. looking for statistics for a research paper
c. writing a synopsis of a play
d. reading a magazine

The correct answer is C. Writing a synopsis of a play.

The synopsis is termed as a brief summary of the whole story. 

The synopsis is different from others like pitch and planning an outline. In synopsis, it is a bit difficult because;
1. Spoiling of the story feels like heresy.
2. Everything in your book seems important.
3. You really want people to like your book.
Synopsis helps a publisher or agent or judge to understand the context of the sample written. It also helps the agent to get the idea of the whole story.

Out of the choices given, the situation where summarizing would be the most useful is writing would be when writing a synopsis of a play. The correct answer is C.