Logically none, because none of them is a watermelon. They're all just parts of watermelons. If the question was how many watermelons were there before they were cut up and assembled like this, the answer is either 5, 6, 7 or 8.
@InOtterWords Ha! There was a logical fallacy in my argument and I thought you were going to point it out, but instead you have been even more pedantic than me, which wins you many gold stars from me! 馃尃馃尃馃尃馃尃馃尃
