Based on a recent study by the National Institute of Health, a

Hello, Rochix123. I can say with near certainty that the answer will not be (D) (provided the OA is accurate, that is). Why? Because if you read the introductory modifier literally, it would be saying that teen-aged boys and girls are based on a recent study, and that makes no sense. We can eliminate answer choices (C) and (E) on the same grounds: neither mass immunization nor the need to mass immunize, or, more basically, a need, can be based on a study. We should only be considering (A) and (B) here. Look at them side by side and remove the parts that overlap. The sentence and answer choices, for reference:

So, we are really looking at a barebones sentence that conveys one of the following:

(A) Based on a study, a conclusion was reached about the need [to do something].
(B) Based on a study, it was concluded that the need exists [to do something].

The passive voice in the original sentence is okay, but I dislike the indirect about. The placeholder it in (B) is grammatically functional and also allows the researchers not to be named. I prefer the straightforward noun clause that the need exists... and the verb form was concluded over the noun a conclusion in the original sentence. If my back were against the wall, I would go for the safer option in (B).

What is the source, Ahmad600? Is there an OA/OE?

- Andrew