What is the difference between abrasion and abfraction?

Abrasion (caused by a foreign object, like aggressive toothbrushing or habits) tends to produce a broader, shallower, flatter or saucer-shaped lesion, while abfraction (caused by occlusal flexural stress) classically produces a deep, narrow, wedge/V-shaped notch at the cervical area. Abrasion is not exclusively cervical (option A is too absolute), abfraction is not limited to posterior teeth, and it's abrasion — not abfraction — that's caused by a foreign element (like a toothbrush or habit).