In Order to Establish a Connection Between an Explanatory and Response

Multiple Choice

In order to establish a connection between an explanatory and response variable in an observational study, what is needed?

A) Statistical methods that examine the connection.
B) A comparison to determine if changes in the explanatory variable are related to changes in the response variable.
C) Either a or b
D) You can never establish a connection between an explanatory and a response variable without doing a randomized experiment.