Jonathan is learning about water conservation. He learns that the average household in the United States uses 293 gallons of water per day. Jonathan makes a chart that shows the percent of water that each indoor fixture uses in the average U.S. household. He would like to use this chart to determine which indoor fixture uses the most water in his own home. Then, he can replace this fixture with a more efficient, water-saving fixture.

What would be an appropriate research question to guide Jonathan's research project?
A) How can we use less water at home?
B) How can the United States conserve water?
C) Which fixture uses the most water in our home?
D) Do shower heads use more water than sink faucets?