Humans have altered the carbon cycle by

A) digging up the stored nutrient resources and combusting them during industrial processes.

B) damming rivers and lakes.

C) increasing the rate at which land based nitrogen is released into the environment.

D) all of the above

D) all of the above

Explanation:these are all correct because they all affect our environment

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).