A Hotel Chain Is Trying to Encourage Its Customers to Reduce

A hotel chain is trying to encourage its customers to reduce their water usage during their stays. Which of the following would be the most effective prompt to reduce water usage?

A) a sign at the registration desk reminding people to use less water
B) a gauge that measures the amount of water people use in comparison with other guests
C) a sign on the bathroom mirror reminding people to use less water
D) a reminder played on the television set to use less water