What can we infer from the statement “His books were as good as medicine.”?

The author is using a simile to compare the books to medicine. Medicine is what you take when you want to feel better. They are suggesting that if you want to feel good, they should read Dr. Seuss’ books.
Choice "His books were in doctor’s office waiting rooms." is incorrect because there is no mention of a doctor’s office. Choice "His books took away fevers." is incorrect because it is using the literal meaning of medicine and the author is using medicine in a figurative way. Choice "His books left a funny taste in readers’ mouths." is incorrect because it makes no sense.