Not surprisingly, there are no professors under the age of eighteen.

Hello, honey1. To answer your last question first, you may want to explore different ways of approaching the same question. Some people will swear by diagramming; others, like myself, write nothing down. But in either case, practice is essential to be able to spot the logical underpinnings of a passage. Consider choice (C) again:


For this to be true necessarily (i.e. to fit a must-be-true condition), we need to find information about voters who are definitely not professors. What does the passage tell us? It is not until the final line that we get any information about brilliant (but not necessarily professorial) people.


To summarize:

1) No professors are under 18.
2) No one under 18 can legally vote.
3.1) Some brilliant people are professors. (Therefore, these brilliant people must be 18+.)
3.2) Some brilliant people are legal voters. (Therefore, these brilliant people must be 18+.)
3.3) Some brilliant people are under 18. (Therefore, this subset of brilliant people must not be professors or legal voters.)

As you can see, we have no information about the voting population, in terms of the professions people hold. We cannot say for certain whether any of these brilliant professors are the same people who comprise legal voters. The term some is too vague. But we can use that same understanding to qualify choice (E), as statement 3.3) shows above.

I hope that helps. I have done the best I can to try to trace my thought process.

- Andrew