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.

explanation:

the fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus eohippus.

explanation:

on disadvantage of hydroelectric power is the cost. another disadvantage of using hydroelectric power is finding a water source powerful enough to harvest hydroelectric power.