Which topic would be most appropriate for a four- to five-page research paper?
are boys and girls different?
do children learn better in boys-only and girls-only schools?
how many boys-only schools are in the us?
are male teachers or female teachers more effective?

The answers is your first option: Are boys and girls different?

Explanation:

Although the topic might seem a bit too simple as a title of a 5-paper research, it is the best option because there are lots of information you can find on different sources as the question doesn't specify exactly the type of differences... you could find information on physical differences, development differences, brain differences, etc...

The other topics would be very short to integrate on a 5-sheet research, as you basically have only one question to answer, and although you could find lots of information with experts' opinions and so, the questions are really closed and you might probably be very repetitive in order to do your five-page research paper.

when completing a research project

explanation:

sufficient and relevant

explanation: