The correct answer is C. motion study.
Motion study is the study of the movements of both the workers and the machine to eliminate wasteful movement. It is a systematic approach to improving the efficiency of work by analyzing and optimizing the movements involved in a task.
Fatigue study is the study of the effects of fatigue on worker productivity. It aims to identify the factors that contribute to fatigue and to develop methods to reduce or eliminate it.
Time study is the measurement of the time required to perform a task. It is used to determine the standard time for a task, which is the amount of time that a qualified worker should take to perform the task at a normal pace.
Work study is a general term that refers to the study of work methods and procedures. It includes motion study, fatigue study, time study, and other methods for improving the efficiency of work.