Which pair of triangles must be similar?
A. Triangles 1 and 2 each have a 35° angle.
B. Triangles 3 and 4 are both isosceles. They each have a 40° angle.
C. Triangle 5 has a 30° angle and a 90° angle. Triangle 6 has a 30° angle and a
70° angle.
D. Triangle 7 has a 50° angle and a 25° angle. Triangle 8 has a 50° angle and a
105° angle.

D) Triangle 7 has a 50° angle and a 25° angle. Triangle 8 has a 50° angle and a  105° angle

Step-by-step explanation:

we know that

If two triangles are similar, then the ratio of its corresponding sides is proportional and its corresponding angles are congruent

Verify each case

case A) Triangles 1 and 2 each have a 35° angle.

There's not enough information

case B) Triangles 3 and 4 are both isosceles. They each have a 40° angle.

There's not enough information (It is necessary to know if the given angle corresponds to the base angle or to the vertex angle in each triangle)

case C) Triangle 5 has a 30° angle and a 90° angle. Triangle 6 has a 30° angle and a  70° angle

The triangles are not similar, because the angles are not congruent

case D) Triangle 7 has a 50° angle and a 25° angle. Triangle 8 has a 50° angle and a  105° angle.

The triangles are congruent

Because

The measure of the angles in triangle 7 are 50°-25°-105° (remember that the sum of the interior angles in any triangle must be equal to 180 degrees)

The measure of the angles in triangle 8 are 50°-105°-25° (remember that the sum of the interior angles in any triangle must be equal to 180 degrees)

therefore

Both triangles have the same angles

That means

Triangles are similar