There are only two plausible answers here, B or A. C and D are impossible because the angle is obviously an obtuse angle, an angle that is greater than 90.
If you're using a protractor, this is rather easy, just use the protractor to measure the angle. If you are not, it gets a bit complicated. I chose A without a protractor because B is only 20 degrees above 90, and it looks too wide to be only 20 degrees above a right triangle.
