Which of the following factors is the underlying cause of dystocia?

Mechanical is the correct answer. This is because dystocia is a very tough, painful, and a prolonged labor which primarily has mechanical factors surrounding the fetus, the uterus, the pelvis, and psyche. While there are other factors such as nutritional factors, environmental factors, and medical factors, that can add up to the mechanical factors that are responsible for dystocia. Dystocia is also referred to as obstructed labor.

This happens when the uterus contracts normally however the baby does not come through the pelvis as it is physically blocked. The baby might not get enough oxygen which can possibly cause death in such cases.