Question

the first carpometacarpal joint is a saddle joint that allows the thumb to perform which motion that the remaining carpometacarpal joints cannot perform: opposition/reposition flexion/extension internal/external rotation abduction/adduction

Explanation:

The first carpometacarpal joint is a saddle joint. Saddle joints allow opposition (touching the thumb to the fingertips) and reposition (returning the thumb to the anatomical position). Other carpometacarpal joints are plane joints which do not allow opposition/reposition. Flexion/extension, internal/external rotation, and abduction/adduction are movements possible at other types of joints (like hinge, ball - and - socket, etc.) but the unique movement for the first carpometacarpal joint (due to its saddle structure) is opposition/reposition.

Answer:

opposition/reposition