Which of the following could be used to slow the pace of a story? a. parallel plot b. short phrases c. flashback d. well-known words

Flashbacks could be used to slow the pace of a story.

Flashback (narrative), in literature and dramatic media, an interjected scene or point that takes the narrative back in time from the current point

The correct answer between all the choices given is the third choice or letter C. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.

the answer is "began" because it is a action that can be done

gregor's attempts to crawl on the walls