Why do scientists think insects are constrained to be relatively small?

They are highly successful clade of organisms. Their breathing system only consists of pair of holes which is called spiracles  along their bodies. They are exoskeleton. Exoskeleton limits the body of an organist to incremental growth through molting. They also found that if the insects are big, hey would be easier to prey upon because they would be more conspiscious. 

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.