Translate：Wheel Flange Lubrication Device. A: 轮辋润滑装置 B: 踏面润滑装置 C: 轮缘润滑装置

The positioning scheme of finish turning the main pin hole is（ ） A: The first positioning datum is the diameter 56 outer cylindrical surface to eliminate 4 uncertainties; the flange end and side surfaces eliminate 1 uncertainty respectively. B: The first positioning datum is the flange end to eliminate 3 uncertainties; the second positioning datum is the outer cylindrical surface with a diameter of 56 to eliminate 2 uncertainties; the side surface eliminates 1 uncertainty