Which of the following statement is incorrect?

A. A force acting in the opposite direction to the motion of the body is called force of friction

B. The ratio of the limiting friction to the normal reaction is called coefficient of friction

C. A machine whose efficiency is 100% is known as an ideal machine

D. The velocity ratio of a machine is the ratio of load lifted to the effort applied

Please do not use chat terms. Example: avoid using "grt" instead of "great".