The nest temperature determines the sex of crocodiles.
Why it is true
As with turtles, the sex of crocodiles is determined by the nest temperature. In crocodiles, lower temperatures produce females and higher temperatures produce males, the opposite of what happens in turtles.
Source: Journal of Zoology
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.