Which of the Following Is True of Sampling

Which of the following is true of sampling?

A) It is the process of gathering data from a subset of the total population, rather than from all members of that particular group.
B) It is a hybrid of primary and secondary research conducted by a research company, spreading the cost across many clients to reduce the price.
C) It refers to the process of identifying what information is needed and how it will be collected.
D) It refers to watching how people behave, either in person or by using a machine to record events.