To prove that STUV is a parallelogram, you need to show that either one pair of opposite sides is equal and parallel or the diagonals bisect each other.
In the context of this question, option d. SO ≅ VO and TO ≅ UO indicates that the diagonals (SU and TV, which go through the center O) bisect each other. This is a property of parallelograms, where the diagonals bisect each other at the midpoint of both diagonals and confirms that STUV is a parallelogram.
So, the correct answer is:
d. SO ≅ VO and TO ≅ UO.