In deep temperate lakes, water temperatures vary according to depth. I

In deep temperate lakes, water temperatures vary according to depth. In winter, the coldest water is at the top; in summer, at the bottom. The changes in temperature distribution, or "turnover," occur in fall and late winter. Lake trout will be found, as a rule, in the coldest water. So, if anglers seek Lake trout in deep temperate lakes while these lakes are partially iced over in late winter, they will do best to eschew the lake trout's summer haunts and fish instead in a shallow bay or close to the surface off a rocky point.

Which one of the following is an assumption on which the argument depends?

(A) The ease with which lake trout can be caught by anglers varies with the time of year and the water temperature.

(B) Cold water is denser, and therefore heavier, than relatively warmer water.

(C) Lake trout are found exclusively in deep temperate lakes.

(D) Lake trout do not alter their feeding habits from one part of the year to another.

(E) In deep temperate lakes that have ice residues on the surface, late-winter "turnover" has not yet occurred.