Please select the best answer from the choices provided.

the answer is C. 60 degrees. The problem says that all three angles equal each other. Since all three angles in a triangle always equals 180 degrees. divide 180 by 3 and you get your answer.
All 3 angles are equal (given) and they also add up to 180 degrees ( they are the angles in a triangle).
So m < D = 180 /3 = 60 degrees (answer)