In what way does crossing over influence the genetic variation of offspring?

A. Genes from both parents are interchanged, which increases the number of possible combinations that the offspring can receive.

B. Chromosomes from both parents are interchanged, which increases the number of possible combinations that the offspring can receive.

C. Genes from both parents are kept separate, which reduces the number of possible combinations that the offspring can receive.

D. Chromosomes from both parents are kept separate, which reduces the number of possible combinations that the offspring can receive.