the question is incomplete
If there is a differnece between two subjects
Simile and imagery
Hughes is using simile in this poem to compare what happens when you put off dreams. He compares deferred dreams to things with very strong sensory imagery like drying up "like a raisin in the sun" or stinking "like rotten meat". These details help the reader understand the heavy impact of what will happen if you put your dreams on hold.
a. three major supporting details.
There are three supporting details for the main idea on the theories to explain why people yawn. Each of the supporting details contains a key word or phrase to indicate that they indeed are a main supporting detail. These key words and phrases are "One explanation is...", "A second theory...", and "Yet another explanation...". These all show the supporting detail is contained in the sentence. The last sentences just build and connect to information that has already been introduced.