In which type of paralysis might an individual retain upper body function while losing the ability to use their legs?

The correct answer is paraplegia. This condition specifically refers to paralysis that affects the lower half of the body, typically including the legs, while the upper body remains functional. Individuals with paraplegia often have intact mobility and sensation in their arms and trunk, which allows them to retain upper body functions.

Quadriplegia, on the other hand, involves paralysis of all four limbs, affecting both the upper and lower body. Hemiplegia refers to paralysis on one side of the body, impacting either the left or right limbs, while monoplegia is a rare condition affecting only a single limb. None of these conditions align with the scenario described in the question, making paraplegia the only appropriate choice.