Geometry

Question Analysis
This question involves converting a biconditional statement into its logical equivalent.
The main focus is on understanding the structure of biconditional statements.

Key Concept Explanation:
A biconditional statement combines a conditional statement and its converse.

Step-by-Step Solution:
The original statement is a biconditional: "A quadrilateral is a parallelogram if and only if its opposite sides are parallel."
This can be split into two parts:
If a quadrilateral is a parallelogram, then its opposite sides are parallel.
If a quadrilateral has opposite sides parallel, then it is a parallelogram.
Option C combines these two parts correctly.

O...