Use Darwin's theory of Natural Selection to explain the process by which the four-legged land animal, A, may have evolved, over about 20 million years, from the fish-like creature, C, in the swampy conditions of the time.

Due to environmental conditions.

Explanation:

With the passage of time, environmental conditions change which causes the evolution of of four legged land animals from fish like creature. This change occurs due to change in environment. In water, there is no need for legs because fish moves with the help of fins and tail but the organisms that lives on land has legs in order to move from one place to another so we can say that change in the physical structure of organism occurs due to environment.

the answer would be 3

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.