Which one from 5 Hexominos fits the fifth box.
Give us your reason why you choose it.
The hexomino that fits in the box is:
The four hexominos in the boxes are cube nets, i.e. they can be folded along the lines so that the squares form the faces of a cube. D is the only one of the choices that is also a cube net.
imagine a grid on each hexamino going from a:1 in the top left corner to c:5 in the bottom right (or f:6, but since there's nothing beyond c line or the 5 line, we won't need it.) Every hexomino in the example has 3 cells in common, a:3, b3 and b4. Of the 3 choices presented, only C satifies this rule.
Here's a picture:
upon actually editing I realised they aren't as aligned as appears at a glance, but here it is:
I'm joking, of course, Wu33o's answer "clicks", in a way this one does not, but you might want to eliminate the ambiguity if it's for anything offcicial.