Which of These Gives an Accurate Example of a Researcher's

Multiple Choice

Which of these gives an accurate example of a researcher's sampling universe?

A) An investigator wants to understand high school drop-out rates, so she draws her sample from all the high school students in her city.
B) An investigator wishes to understand parents' vaccination decisions, so he reads a selection of papers already published on the anti-vaccination movement.
C) A researcher hopes to explain the relationship between divorce rates and religious belief, so she interviews one divorced couple about their faith.
D) A researcher plans to teach safe sex to teens, so he provides leaflets and workshops to local clinics.