For two variables in a direct proportion, what is the result of doubling one variable? the other variable is doubled the other variable is halved the other variable stays constant

According to the passage, which of these is true about gray water systems? a) gray water systems use plants that require less water. eliminate b) gray water systems require the use of less fossil fuels. c) gray water systems reduce the amount of fresh water used. d) gray water systems reduce the amount water used by shower heads.