There is only one correct sentence, and you should choose one which you believe is right.
A.
Population refers to some of set of persons that have at least one common characteristic of interest to the researcher.
B.
Sample is a smaller, unmanageable version of a larger group.
C.
Sampling is a process used in statistical analysis in which a predetermined number of observations are taken from a smaller population.
D.
Sample design refers to the plans and methods to be followed in selecting sample from the target population and the estimation technique formula for computing the sample statistics.