To describe a rectangle, the following properties can be identified:
A) All angles are acute - False. In a rectangle, all angles are right angles (90 degrees), so they cannot be considered acute.
B) Opposite sides are perpendicular - False. In a rectangle, opposite sides are parallel, not perpendicular.
C) Opposite sides are parallel - True. This is a defining characteristic of rectangles.
D) All sides are the same length - False. This describes a square, which is a specific type of rectangle, but not all rectangles have equal side lengths.
Based on the above analysis, the correct answer is C) opposite sides are parallel.