The correct option is A Smooth muscle fibre
Smooth
muscle fibres or cells are elongated and spindle-shaped. The main
function of these muscle fibres is peristalsis. It happens in tubular viscera.
That’s why smooth muscle fibres are present in the wall of the alimentary canal. These are involuntary muscles. The autonomous nervous system controls the action of these muscles. Thus, they are
not under the control of one's will.