The metacarpals articulate with the
a. proximal carpals
b. phalanges
c. ulna
d. radius

b. Phalanges

Explanation:

The metacarpals are the five bones that form and support the hand and articulate distally with the proximal phalanges, the bones that form the fingers, and proximally with the distal carpals. The carpus is composed of eight bones that connect the hand with the forearm, those bones are divided into distal and proximal, distal means far from the midline and proximal means near to it. Therefore, the distal part of the carpus is the one that articulates with the metacarpals.

The ulna  and the radius are the bones that form the forearm and articulate with the proximal carpals.