Ding ding, I'm here again! ΔABC is an isosceles right triangle. Use the isosceles triangle base angles theorem and the sum of the interior angles of a triangle to determine the measures of ∠ACB and ∠ABC.

A: ∠ACB = 90° and ∠ABC = 45°

B: ∠ACB = 45° and ∠ABC = 90°

C: ∠ACB = 90° and ∠ABC = 90°

D: ∠ACB = 45° and ∠ABC = 45°

Answer : D

Since we know that they are both right triangles, we can automatically assume that the angle measures are going to be 90°,45°,45°.

We can use this information to identify the angle measures of ACB and ABC.

These angles are both located at the 45° positions of the triangle, therefore the both have angle measures of 45°.

The answer is d., a mountain.