Concept:This question tests the ability to choose a word that is opposite in meaning to the underlined word and that fits the context of the sentence.
Explanation:The underlined word is "improved", which means became better.
The sentence states: "We thought that Uncle Sam's health had improved but it had rather..."
The word "but" indicates a contrast, so the missing word must mean the opposite of "improved", that is, became worse.
Now examine the options:
A. "persisted" means continued, which is not opposite.
C. "deepened" means became deeper, not a suitable opposite.
D. "decreased" means became less, which does not fit the context of health.
B. "deteriorated" means became progressively worse, which is exactly the opposite of "improved" and correctly completes the sentence.
Therefore, the correct choice is option B.
Answer:B. deteriorated