Question: Should the legal drinking limit be lowered to 18?
Population: People in the United States of America under 35
Parameter of interest: the proportion of people who believe the drinking limit should be lowered.

Asking people in the under 21 clubs across the country whether the legal limit should be lowered.
"Drinking is one of the leading causes of death. Should the legal drinking age be lowered?"
Giving out a Facebook survey asking if the limit should be lowered.
Posting sign-up sheets near bars on a survey for whether or not the legal drinking age should be lowered.