Which of the following is the most appropriate unit to describe the rate at which water flows over Niagara Falls?

A: Day per billion gallons, because the independent quantity is volume of water in billion gallons and dependent quantity is time in days

B: Billion gallons per day, because the independent quantity is volume of water in billion gallons and dependent quantity is time in days

C: Billion gallons per day, because the independent quantity is time in days and dependent quantity is volume of water in billion gallons

D: Day per billion gallons, because the independent quantity is time in days and dependent quantity is volume of water in billion gallons

Respuesta :

C) Billion gallons per day, because the independent quantity is time in days and dependent quantity is volume of water in billion gallons.

Hope this helps!!
Here "rate" refers to how much water in how much time, so eliminate A qnd D.  Which sounds correct, B or C?  The correct answer corresponds to 
(quantity of water) / (period of time).