In the Deep Layer of the Palm the Dorsal Interosseous

In the deep layer of the palm the dorsal interosseous muscles insert into:

A) the medial side of the base of the proximal phalanx of the thumb
B) flexor tendon mechanisms of digits 2, 3, 4, and 5
C) extensor expansions of digits 2, 3, and 4
D) bases of proximal phalanges 2, 4, and 5
E) bases of middle phalanges 2, 3, 4, and 5