The bases for a cylinder must be two discs that are parallel and:A.similar.B.squares.C.have one lying directly above the other.D.congruent.

The correct answer is D. Congruent.

Here's why:

A. Similar - This term is usually used to describe two figures that have the same shape but not necessarily the same size. However, in the case of a cylinder, the two bases must be exactly the same size, not just similar in shape.

B. Squares - This is incorrect because the bases of a cylinder are circles, not squares.

C. Have one lying directly above the other - While it's true that one base of a cylinder is directly above the other, this statement doesn't describe the relationship between the two bases. It's more about their position in space.

D. Congruent - This is the correct answer. In geometry, "congruent" means that two figures have the same size and shape. Since the bases of a cylinder are two circles of exactly the same size, they are congruent.