What does it mean that Gatsby knew when to stop "? Help ASAP

What is the authors purpose in writing this paragraph

Read the sentence: though margo moved as slowly as a snail in the morning, she somehow ended up being the shining star at the corporations breakfast meeting. which phrase from the sentence is an example of the authors use of simile? a) being the shining star b) somehow ended up c)the corporations breakfast meeting d)moved as slowly as a snail

Which example shows the correct way to cite a book on an mla works cited page?