Question

researchers periodically survey a few thousand of the patients taking a certain medication in order to make connections between that medication and the subjects general health. this method of gathering data is classified as a census. a sample survey. an experiment. an observational study.

Explanation:

A census involves surveying an entire population. Here, only a few thousand patients out of all taking the medication are surveyed, so it's not a census. An experiment involves manipulating variables. No manipulation is described here. In an observational study, researchers observe and collect data without interfering. A sample survey is a type of observational study where a sample of the population is surveyed. Since a subset of patients is being surveyed to gather data about the relationship between the medication and general health without interference, it's a sample survey.

Answer:

B. a sample survey