The topography of each basin determines the area that it drains and whether that water exits into...
a. The Gulf of Mexico and the Pacific Ocean
b. The Gulf of Mexico
c. The Atlantic Ocean
d. The Atlantic Ocean and the Gulf of Mexico

i'll try what topic lol

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).

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.