If you didn't need to explain you could say it is a rhombus since if u turn ur head a little its slanted, but you do so heres how. there are at most 2 right angles!!!!!! since squares and rectangles all have 4 right angles, and there are only 2 undefined angles in the shape you can eliminate the other 2 answers of square and rectangle. And if you do the math (the sum of all the angles in a triangle is 180) you will find that the other two angles arn't even right angles! so there you have it.
