When children are young and go to the doctor, the doctor will give them booster shots. This re-exposes the children to a dead portion of a disease to help them build immunity. Which type of immunity is described?

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.