Answer: (B) rhombus
Let □ABCD touch the circle. Tangent segments from an external point are equal, which gives AB + CD = AD + BC.
In a parallelogram AB = CD and AD = BC, so 2AB = 2AD, i.e. AB = AD. A parallelogram with adjacent sides equal is a rhombus.
A square is a special rhombus, but the parallelogram need not have right angles, so the answer that must be true is rhombus.