下列加工工序中 不是自为基准加工的。 Which of the following operation is not based on self-datum principle

A、浮动镗刀镗孔A floating boring cutter bores holes;
B、无心磨床磨外圆A centerless grinder grinds the cylindrical surface;
C、齿轮淬火后磨齿面 Grinds the tooth surface after quenching of the gear;
D、浮动铰刀铰孔The floating reamer reams the holes