I got Private Messaged to answer this question, and indeed, the discussion has been long and fruitful! What fun!
The fear of rabies is well founded; few people are known to recover from the disease after the appearance of the clinical symptoms.
(A)few people are known to recover from the disease after the appearance of the clinical symptoms.
PROBLEM: This question is a classic concision trap. The hope is that you'll pick A, thinking that A and B are the same and this one is shorter. But this is not idiomatic. We say "SUBJECT is known TO HAVE RECOVERED" not "SUBJECT is known TO RECOVER." We wouldn't say he is "known to eat twenty apples". The present tense infinitive (to eat) is wrong. Correct is that "I am known to have eaten 20 apples", which correctly uses the present perfect to imply this is what we've known from the past into the present.
Also, "after" and "once" have slightly different meanings. "I'm going to the store after lunch" implies that SOMETIME after lunch, I'll go to the store. "I'm going to the store once I've eaten lunch" implies that there is a causal relationship between the eating and the going to the store, that eating lunch is the threshold. That's what we want here, because the symptoms are the threshold.
(B)few people are known to have recovered from the disease once the clinical symptoms have appeared
(C)there are few known people who have recovered from the disease once the clinical symptoms have appeared
PROBLEM: Adjective "known" is now modifying "people", which is silly.
(D)after the clinical symptoms appear,there are few known people who have recovered from the disease
PROBLEM: Same as above, and the placement of the prep phrase "after..." is odd.
(E)recovery from the disease is known for only a few people after the clinical symptoms appear
PROBLEM: "Known for only a few people" doesn't make any sense. It's not that the recovery isn't known, but that few people are known to have recovered.
Hope that helps! The answer is definitely B.
Tommy Wallach | Manhattan GMAT Instructor | San Francisco
Manhattan GMAT Discount | Manhattan GMAT Reviews