5. If the parallel lines $E F, M N$ intersect with the intersecting lines $A B, C D$ to form the figure shown, then the number of pairs of alternate interior angles is ( ).
(A) 4
(B) 8
(C) 12
(D) 16
5. Since each "three-line eight-angle" basic figure contains two pairs of consecutive interior angles, and from the given figure, the following 8 basic figures can be decomposed, there are a total of 16 pairs of consecutive interior angles.