Which of the following statements is not correct ?

A. In the knee-jerk reflex, stimulus is the stretching of muscle and response is its contraction

B. An action potential in an axon does not move backward because the segment behind is in a refractory phase

C. Depolarisation of hair cells of cochlea results in the opening of the mechanically gated potassium-ion channels

D. Rods are very sensitive and contribute to daylight vision