Healthy Person X is walking on level ground.  Which of the following is true for the knee extensor muscle of X's right leg during the step cycle?

A. The right knee extensor muscle has a shortening contraction near the end of the right leg's swing phase just prior to start of the right leg's stance phase.

B. Just after the right foot touches the ground at the start of stance phase, the sum of the lengths of all the overlap regions between the thick and thin filaments (= the region of the A band not in the H zone) will decrease in the right knee extensor muscle.

C. Just after the right foot touches the ground at the start of the stance phase, the sum of the lengths of all the H zones will decrease in the right knee extensor muscle.