17-189 As shown in the figure, in the acute triangle $\triangle ABC$ with unequal sides, the three altitudes $AD$, $BE$, $CF$ intersect at point $H$. Then the number of different shapes (non-similar) triangles in the figure is
(A) 6 kinds.
(B) 7 kinds.
(C) 9 kinds.
(D) 10 kinds.
(China Junior High School Mathematics Correspondence Competition, 1990)
[Solution 1] In the figure, there are 16 triangles of different sizes, which are $\triangle A B C, \triangle A F H$,
$$
\begin{array}{l}
\triangle F H B, \triangle B H D, \triangle H D C, \triangle C E H, \\
\triangle A E H, \triangle A B E, \triangle A C F, \triangle B E C, \triangle B F C, \triangle A B D, \\
\triangle A D C, \triangle A H B, \triangle A H C, \triangle B H C .
\end{array}
$$

Among them, there are 9 pairs of similar triangles, which are
$$
\begin{array}{c}
\triangle B H D, \triangle B C E ; \triangle A H E, \triangle A C D ; \triangle B H F, \triangle B A E ; \\
\triangle A F H, \triangle C D H ; \triangle F H B, \triangle E H C ; \triangle A H E, \triangle B H D ; \\
\triangle A B E, \triangle A C F ; \triangle B E C, \triangle A D C ; \triangle B F C, \triangle B D A .
\end{array}
$$

Therefore, there are 7 different shapes of triangles in the figure.
So the answer is $(B)$.
[Solution 2] In the figure, there are three types of non-similar triangles:
(1) $\triangle A B C$;
(2) $\triangle A H F, \triangle B H D, \triangle C H E$;
(3) $\triangle A H B, \triangle B H C, \triangle C H A$.

In total, there are seven types.
So the answer is $(B)$.