Which of the following conditions enhances the effectiveness of "plunging fire"?

Plunging fire is a method of firing that occurs when the line of fire descends steeply toward the target. This technique is particularly effective when the shooter is positioned at a high elevation, allowing the bullets to travel downward at a steep angle, which can enhance accuracy and lethality against targets below.

When firing from a high elevation, the shooter can take advantage of gravity, which can help to increase the bullet's impact upon reaching the target. Additionally, the angle of attack makes it more challenging for enemies to return effective fire, as they might be shooting upward at a less favorable angle. The use of high ground is a key tactical advantage in military operations, especially when employing plunging fire, making this condition particularly beneficial for effective engagement of enemy forces.

In contrast, flat terrain does not provide the same advantage as it lacks elevation for effective plunging fire. Close enemy engagement may lead to unpredictability and increased risk of friendly fire as targets are often within direct line of sight. Protected lines of sight are crucial for effective targeting but do not specifically enhance the plunging nature of the fire like high elevation does. Thus, the condition that most significantly enhances the effectiveness of plunging fire is being at a high elevation.