Your answer would be D. 30 degrees. Hope I helped you!
Here's why:
Answer A. 50 degrees is NOT the choice because the angle is smaller than 50 degrees, but not by much.
Answer B. It's not obtuse, so we can already cross that one off.
Answer C. It's not obstuse, just like the previous one, so this is one is immediately off.
Answer D. The best choice and the correct answer.