Which of the Following Was Not One of the Methodological

Which of the following was not one of the methodological approaches used by researchers in the National Health and Social Life Survey?

A) They selected households with eligible subjects in randomly chosen areas of the country.
B) They attempted to interview all eligible members of the household in each of the households selected.
C) They gathered data through face-to-face interviews conducted by trained survey researchers.
D) They sometimes returned to households several times to persuade all of the desired participants to cooperate with the interviews.