【Question 5】
Two line segments are parallel, forming a pair of parallel line segments. As shown in the figure, among the 12 edges of a rectangular prism, there are $\qquad$ pairs of parallel line segments.
【Analysis and Solution】
The 4 lengths of the rectangular prism are parallel to each other, with $C_{4}^{2}=\frac{4 \times 3}{2 \times 1}=6$ pairs of parallel line segments; similarly, the 4 widths of the rectangular prism are parallel to each other, and the 4 heights of the rectangular prism are parallel to each other; there are a total of $6 \times 3=18$ pairs of parallel line segments.