Which of the following is not a unique characteristic of a bird?
a. most lay their eggs in the water.
b. most can fly.
c. they have feathers.
d. they walk on two legs.

well, you see. the answer to your question is quite simple. the thing that is big, powerful, and over 9,000 is your mom.

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.