Stressor is a(n) select one: a. exercise program that increases one's ability to handle normal stress. b. hormone released by the adrenal glands during periods of stress. c. lower back muscle that frequently produces a feeling of physical tension. d. environmental event that threatens or challenges us.

The correct answer is d. environmental event that threatens or challenges us.

A stressor is any event that causes stress to an organism such as biological agent (bacteria or virus) or environmental stimulus (changes in temperature). It can also be social (family problems), workplace (problems at work) or daily (some challenge).

The answer would be c, white eyes are homozygous recessive. in the early 1900s, morgan conducted several experiments with vinegar  flies (drosophila). one  sample revealed an anomaly: a  white-eyed, single male fly. he attempted to breed this fly with the typical red-eyed females. the offspring were all red-eyed. using flies from this new generation (brother-sister pairs)  produced some red-eyed and a few white-eyed flies. the white-eyed were all male. in later experiments, he was able to produce white-eyed females. this proved that white eyes are not lethal to either sex (ruling out a and b). since the percentage of white eyes to red eyes is so low, white eyes are not a dominant trait. it would be a recessive trait.