Acombined sewer system to a sewage treatment plant. a. household waste water b. rain water c. lawn run of d. all the above

The answer is D.

Explanation:

Sewers are connected to households and usually roads. When rain comes down, it goes down the drain in the road which leads to the sewers. The same thing happens with the answer C. A, household waste water, is connected to the sewers as well. So, since all three of these are correct, you would choose D.

Hope this helps.

rain is the best answer