ANSWER:
If this is a lesson about past, present and future tenses, then the answer would most likely be
FLOCKED
which is a past tense of flock.
I strongly believe that it is B. I know it isn't D because it doesn't compare or contrast asthma to something else.
Answer:
The term that you are looking for is Imagery.
Hope this helps!
Between grass and felt. at a comma to either end of the phrase to make it gramatically correct.