is the ans E?

In the passage, the author concludes that the frog population decline is probably due, at least in part, to the ultraviolet radiation increase.
The author assumes that since the eggs are not shell type but are gelatinous, they are damaged by radiation.

We are asked to find the support for argument.(Radiation is somewhat responsible for the damage) It's a strengthen type question.

(A) Even in those regions where there has been no significant increase in ultraviolet radiation, only a small proportion of the frog eggs that are laid ever hatch. - This tells us that some other factor is responsible for the decrease. Out of scope

(B) In areas where there has been the least decline in frog populations, populations of species of insects that frogs eat have decreased. - insect population decrease : Irrelevant

(C) The eggs of frog species whose populations are declining tend to have higher concentrations of damaging pesticides than do the eggs of frog species whose populations have not declined. - pesticides are responsible but not radiation : wrong

(D) In many places where turtles, which lay eggs with tough, leathery coverings, share habitats with frogs, turtle populations are also in decline. - irrelevant

(E) Populations of frog species that hide their eggs beneath rocks or under sand have declined considerably less than have populations of frog species that do not cover their eggs. - This tells us that the eggs that are covered with rock or send remain safe and those that aren't are damaged due to ultraviolet radiation.