Which of the Following Is True of Probability Sampling

Which of the following is true of probability sampling?

A) It includes a large sample of respondents that voluntarily completes questionnaires on a regular basis so that researchers can assess changes in behaviour and attitudes.
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 involves precise rules to select the sample so that each element of the population has a specific known chance of being selected.
D) It involves the use of arbitrary judgment by the market researcher to select a sample so that the chance of selecting a particular element of the population is either unknown or zero.