$17 \cdot 192$ As shown in the figure, $E, F$ are the midpoints of sides $AB, AC$ of $\triangle ABC$, respectively. Then, the number of pairs of triangles with equal area in the figure is 
(A) 10 pairs.
(B) 9 pairs.
(C) 8 pairs.
(D) 6 pairs.
(China Sichuan Province Junior High School Mathematics Competition, 1988)
［Solution］The triangles with equal areas in the figure are:
$$
\begin{array}{lll}
\triangle A B F, \triangle C B F ; & \triangle A C E, \triangle C B E ; & \triangle B E F, \triangle C E F ; \\
\triangle E B C, \triangle F B C ; & \triangle E O B, \triangle F O C ; & \triangle A B F, \triangle A C E ; \\
\triangle A F E, \triangle B F E ; & \triangle A E F, \triangle C E F ; & \triangle A C E, \triangle B C F ; \\
\triangle A B F, \triangle B C E . & & \\
\text { A total of } 10 \text { pairs. } & \\
\text { Therefore, the answer is }(A) . &
\end{array}
$$