This is definitely a tricky question, but it actually is not too hard once you see the pattern. As you know, the LSAT is all about recognizing patterns.

The concept is as follows:

Basically, even though 1984 is the 2nd most influential book, it may be a very distant second (and probably is IMHO). So, it is quite possible that The Bible was the most influential for 95% of people surveyed and that 1984 was the second most influential by influencing, let's say 3%. And 2 other books influenced 1% of the surveyed people.

This would satisfy the conditions, but, obviously, in this situation, the book 1984 did not influence a great number of the readers. Rather, it influenced a small number (30 of the 1,000 readers surveyed to be exact).

Conversely, it is possible (though not likely IMHO) that the Bible could have influenced only something like 50% of the readers and that 1984 influenced 45% and a compilation of other books each influenced the rest of the 5% of readers. In this situation, The Bible influenced 500 of the 1,000 readers and the book 1984 influenced 450 of 1,000 the readers. So, in this second case, the book 1984 did in fact influence a large number of readers.

As such, understanding how many of the readers chose the book 1984 can help you understand how strong the argument is. Unfortunately, that is not one of the answer choices. So, then you have to evaluate the answer choices and see if any of them will help you obtain this same information in a slightly more round-about way. And indeed, answer choice (B) does precisely this. Because if you can find out how many books other than 1984 influenced the readers surveyed, then you can help you to ascertain whether or not 1984 actually influenced a large number of readers.

Does this make sense? I hope this explanation helps.

:)Lisa