In its short history, the art of motion pictures has frequently undergone change that seemed fundamental, ______ the introduction of sound.

A．such as which resulting from

B．such as that what results from

C．such as that resulting from

D．such as which results from

一般情况下，速度继电器有两对常开触点和两对常闭触点，当电动机带动其转子向某方向运行达到某一转速时，有一对常开触点接通，常闭触点断开，所以速度继电器可以用于电机的制动控制。