Correct Answer: A
Explanation:
The author has “damaged” eyes, and any word that fills the blank must reflect that fact.
The words that best do so are “deteriorate” and “decline” (Choices A and D), which generate
sentences alike in meaning. “Sharpen” and “improve” produce sentences alike in
meaning, but neither word makes sense when inserted into the blank. Though “adjust”
makes some sense when inserted into the blank, no other option produces a sentence
similar in meaning.