Which is an example of how bacteria help keep the environment clean?
They can reduce oxygen in the air.
They can decompose waste.
They can help develop medicines.
They can slow digestion.

They can decompose waste.

Explanation:

they decompose a worm, for example, and then it is good for the soil

c. would be the answer : )

explanation:

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).