In order to keep the soil fertile, farmers often change the crop that is grown in a field every two to three years. What is this process called?
A.
sharecropping
B.
crop conservation
C.
organic farming
D.
crop rotation

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.

Why does the earth spin slowly, not faster? is it possible to prove it scientifically? can you prove it with math?

The image shows a group of fish. the type of social behavior shown in the image is called