Time and motion studies' refers to:

a) the process in which managers use their judgment to estimate the time it takes to carry out each individual work task, in order to estimate cost
b) the process in which employees complete timesheets each day; the timesheets then form the basis for cost estimation
c) the process in which employees are observed when they undertake work tasks; these observations are then used to estimate cost
d) the process in which the cost of work tasks are compared over time and across different divisions