18.2 If the angle bisectors of $\angle B A D$ and $\angle B C D$ in quadrilateral $A B C D$ are parallel, then the relationship between $\angle B$ and $\angle D$ is
(A) $\angle B=\angle D$.
(B) $\angle B$ and $\angle D$ are supplementary.
(C) $\angle B>\angle D$.
(D) $\angle B<\angle D$.
(China Beijing Junior High School Mathematics Competition, 1991)
[Solution] Let $A E, C F$ be the angle bisectors of $\angle B A D$ and $\angle B C D$ of quadrilateral $A B C D$, respectively, and $A E \parallel C F$. Then
$$
\begin{aligned}
\angle D & =180^{\circ}-(\angle 1+\angle 6) \\
& =180^{\circ}-(\angle 2+\angle 3) \\
& =180^{\circ}-(\angle 5+\angle 4)=\angle B,
\end{aligned}
$$

Therefore, the correct choice is $(A)$.