Human sperm cells and egg cells area haploid, each containing 23 chromosomes. b haploid, each containing 46 chromosomes. c diploid, each containing 23 chromosomes. d diploid, each containing 46 chromosomes.

A. haploid, each contain 23 chromosomes.

Explanation:

A egg and sperms are formed after reduction division or meiosis and hence carry just 23 chromosomes , a single copy after division. the number is restored back to 46 after the fusion of egg and sperm to form a zygote.

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme

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).