Which three statements about a rhombus are true?

A. it could not be a rectangle

B. it could be a trapezoid.

C. it must be a square

D. it must be a parallelogram

E. it could not be a Pentagon

A rhombus have four sides and all sides are equal with opposite sides are parallel.

So, since it have four sides, so it could not be a pentagon. Since opposite sides are parallel and equal, so it must be a parallelogram. And since all sides are equal, so it must be a square and it could not be a rectangle.

Therefore correct options are A, C, D, E.