"Pull-Ups" Are Easier to Do with the Hands Supinated Than

Multiple Choice

"Pull-ups" are easier to do with the hands supinated than with the hands pronated. An explanation for this is

A) the biceps brachii is attached to the radial tuberosity.
B) the biceps brachii supinates the forearm.
C) if the forearm is pronated, the biceps brachii is ineffective in flexing the forearm.
D) the brachialis is a much smaller muscle than the biceps brachii.
E) All of these contribute to a full and proper explanation.