Answer:
The answer is D.90°
Step-by-step explanation:
In this case, every measure has to be defined by three points and the vertex of this measure is in the middle point. The angle that is formed between two rays with the same endpoint is measured in degrees. The extreme points form the rays and the middle point is the vertex.
For example, if we want to know the measure ∠ABC, we have to located the points A, B and C, in the same order. Then the rays are in the same direction that A and C, and vertex will be in the point B (the middle one).
Also, there are some definitions for different range of angle measure. I have attached an image that show some definitions.
Finally, the measure ∠QRS corresponds to a right angle (It has the same notation that in the attached image).
Therefore, the measure ∠QRS is 90°