Factors that make an ecosystem stable

Explanation:

factores  físicos  son  la  luz  solar , el  suelo ,  el  agua ,  los  nutrimentos , la  temperatura , y   el  aire

i think it would be b. tissue because an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.

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).