Answer:
The angle DCF is the right angle (D.).
Explanation:
Usually, the right angles are marked with a small square, so if you see that, it means that is a 90º angle, no questions asked. :]
Answer A. says ECF, but that is only one of the two angles that add up to make the 90º angle.
Answer B. is not an angle at all. They should come with a slanted L and 3 letters to indicate an angle.
Answer C. says DCE, but that is just the other angle that adds up to make the 90º angle.
So that means Answer D. is the correct answer!