Which class of machine gun fire is categorized as grazing fire?

Grazing fire is characterized by the trajectory of the bullets flying just above the ground and is generally classified based on the respect to ground. In this case, the correct choice indicates that grazing fire occurs when the line of sight of the bullet path is at a height less than two feet off the ground and remains in a horizontal position. This type of fire is effective for engaging targets that are either lying prone or low to the ground, as it minimizes the chance of the rounds ricocheting and increases the lethality on the target.

In contrast, the other options represent different classes of machine gun fire that have varying characteristics. For example, respect to ground classifications that do not fit the definition of grazing fire, such as 1/2 and those based on either respect to target or terrain, do not align with the fundamental principle of grazing fire. Thus, knowing that grazing fire is specifically categorized as 2/2 respect to ground reinforces the understanding of machine gun employment and tactics in infantry operations.