Which figure shows the outline of the folded paper when a square sheet is folded first along line 1 (left half over onto the right half) and then, on the folded half, along line 2 (the bottom-right corner turned up over the paper)? The dotted square marks where the open sheet was.

Fold 1 leaves the right half. Crease 2 runs from the middle of the bottom edge to the middle of the right edge, so fold 2 turns the bottom-right corner up onto the paper and cuts that corner off the outline: a four-sided shape with corners at the top-left and top-right of the right half, the middle of the right edge and the middle of the bottom edge, which is (a).