What can we say about machines and engines?
A. Friction increases fuel efficiency.
B. There is no friction.
C. The process of overcoming friction uses
valuable fuels.
D. Friction is unlikely.

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.