4. As shown in Figure 1, in quadrilateral $ABCD$, adjacent sides and angles are not equal, $E$ and $F$ are the midpoints of $BO$ and $DO$ respectively. Then, the number of pairs of congruent triangles in this figure is ( ).
(A) 5
(B) 6
(C) 7
(D) 8
4. C.

According to the figure, there are 7 pairs of congruent triangles.