18. The figure below is a symmetrical figure with the axis of symmetry being $\mathrm{AF}$, then the number of pairs of congruent triangles in the figure is ( )
(A) 5 pairs
(B) 6 pairs
(C) 7 pairs
(D) 8 pairs
Answer: (C)
Solution: There are 5 small triangles above the axis of symmetry. According to the properties of symmetry, there are corresponding congruent triangles below the axis of symmetry;

In addition,
$$
\triangle \mathrm{ABC} \cong \triangle \mathrm{ADE},
$$
$\triangle \mathrm{AEM} \cong \triangle \mathrm{ACN}$ ( $\mathrm{M}$ is the intersection of $\mathrm{AC}$ and $\mathrm{DE}$, $\mathrm{N}$ is the intersection of $\mathrm{BC}$ and $\mathrm{AE}$ ),
there are a total of 7 pairs of congruent triangles,