Explanation

Otherwise suggests that Gottlieb did not find Steinbeck’s political views admirable. “Adolescent disaffection” suggests that he found Steinbeck’s views in some sense immature, so look for negative words that mean something like “immature.”

Naïve and callow are the best options. Perspicacious and keen both suggest insight, nearly opposite of what we’ve anticipated. Contemptible is negative, but with no suggestion of immaturity — make sure to use the clues provided without adding your own ideas. (Note that naïve is sometimes written with two dots over the “i,” as in the original French, and sometimes without.)

Hence Naïve, callow are best fit!