A triangle is split by one line from its apex to the base, and crossed by two lines parallel to the base.

Explanation

1. 01

   From the top vertex there are 3 lines in all: the two sides and the 1 inner line. Any 2 of them form a triangle with a horizontal line as the third side.

2. 02

   Pairs of lines from the vertex: $\binom{3}{2} = 3$.

3. 03

   Horizontal lines that can close them: 3 (the base and 2 parallel lines).

4. 04

   Triangles $= 3 \times 3 = 9$.