Given Data

1. Target: a smaller triangle sharing one side with a larger triangle.
2. Option C has a large triangle with an internal line from its top vertex to the midpoint of its base.

Question

Why does Option C contain the target?

Answer

The internal line and one outer side create the smaller required triangle.

Solution

1. Use the top vertex, the internal line, and the left half of the base.
2. These three segments form the target triangle inside the larger one.
3. The remaining outer lines are extra details and can be ignored.