The average age of university presidents in a large sample

OFFICIAL EXPLANATION:

From a study of the average ages of university presidents in ‘a large sample of universities’ a general conclusion has been arrived at, which is then presumed to be applicable to all universities.

We have been asked to identify that choice which would cast the most doubt on this conclusion. Since the question asks for the answer that casts the most doubt, one of the answers must be chosen and answer (E) none of the above is incorrect.

We should therefore look for that statement which implies that the sample universities studied did not represent the majority of universities in some important respect, and that it is therefore unscientific to arrive at a general conclusion based on this unrepresentative sample. (A ‘large sample’ may still constitute a minority of the total number of companies.)

The phrase ‘in those same universities 20 years ago’ in the third line of the passage implies that the companies taken up for the sample study were limited to those which have been operating for more than 20 years. If a many of the existing universities (including online universities) are, in fact, less than 20 years old, the phenomenon prevailing in the older universities cannot be inferred as being applicable generally to all universities. It is quite likely that the average age of the university presidents of newer universities is much less than 57.

It is (C) which implies this, and is the answer.