An independent variable is a. directly changed by the experimenter. b. manipulated by changes to the dependent variable. c. a variable that is kept constant. d. a variable that is used as a control. select the best answer from the choices provided

A) Directly changed by the experimenter  

Explanation:

In mathematical modeling, analytical modeling and experimental sciences, the values of dependent variables depend on the values of independent variables. The dependent variables describe the output or outcome whose change is being examined. An independent variable seldom named an experimental or predictor variable, is a variable that is being formed in an experiment in order to inspect the impact on a dependent variable, sometimes described as an outcome variable.

sadness is not good

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).