A circuit is open when... A. the switch is incomplete
B. the light bulb is lit
C. the circuit is incomplete
D. a buzzer is used instead of a light bulb

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).

for a different answer set the answer would be because the oxygen in the water had depleted (apex)