Select the statement that expresses an approach used with observational studies.

A. "We took all those notes. We recorded customer counts, menus, food prices, even the general atmosphere of the food truck environment."
B. "Next week, let's send out a coupon for 25% off any menu item to see if we get more customers."
C. "We can test out locations for a brick-and-mortar store by moving our truck. I mean, we have our social media page that gives our daily locations, but what if we find a location we like for a brick-and-mortar store and see if our customers follow us there?"
D. "I think asking questions and collecting the information we want from our population sample is a good start."