Pretty sure its C Â >:]
Explanation:
  It's the third option because if you put a piece of paper in the corner its a lil more than 90 degrees, so it wouldn't be B (there's a little more white space left). And it obviously wouldn't be A because that's self explanatory, lol.
  And you can't make a perfect square in the inside of the angle so that's another way to tell.
Extra:
I hope you have an amazing day too,, you seem very nice ^-^ Â good luck on your schoolwork today :]