The H-zone in the skeletal muscle fibre is due to
A. the central gap between myosin filaments in the A-band.
B. the central gap between actin filaments extending through myosin filaments in the A-portion of the A-band .
C. extension of myosin filaments in the central portion of the A-band .
D. the absence of myofibrils in the central portion of A-band.