Select the odd pair.

The correct answer is the pair featuring a vertical rectangle on the left and 4 horizontal lines on the right:

To determine the odd pair among the options, let us examine the geometric relationship between the number of sides of the polygon on the left and the number of horizontal line segments (with arrowheads) on the right for each pair:

1. First Pair:
The polygon on the left is a triangle, which has 3 sides.
The figure on the right consists of 2 horizontal lines.
Pattern:

$\text{Number of lines}=\text{Number of sides}-1=3-1=2$

2. Second Pair:
The polygon on the left is a pentagon, which has 5 sides.
The figure on the right consists of 4 horizontal lines.
Pattern:

$\text{Number of lines}=\text{Number of sides}-1=5-1=4$

3. Fourth Pair:
The polygon on the left is a horizontal rectangle, which has 4 sides.
The figure on the right consists of 3 horizontal lines.
Pattern:

$\text{Number of lines}=\text{Number of sides}-1=4-1=3$

4. Third Pair:
The polygon on the left is a vertical rectangle, which has 4 sides.
The figure on the right consists of 4 horizontal lines.
Pattern:

$\text{Number of lines}=\text{Number of sides}=4$

In three of the pairs, the number of horizontal lines on the right is equal to the number of sides of the shape on the left minus 1. The third pair violates this rule because it has 4 horizontal lines for a 4-sided shape. Thus, it is the odd pair out.