普通麻花钻的背吃刀量为（）（dm为工件已加工表面直径）。
A.
B.
C.
D.
参考答案：B
已知Ag2SO4的Kw为2.0×10-3，将适量Ag2SO4固体溶于100 mL水中至刚好饱和，该过程中Ag+和SO42-浓度随时间变化关系如图〔饱和Ag2SO4溶液中c(Ag+)＝0.034 mol·L-1〕。若t1时刻在上述体系中加入100 mL0.020 mol·L-1 Na2SO4溶液，下列示意图中，能正确表示t1时刻后Ag+和SO42-浓度随时间变化关系的是
A．
B．
C．
D．
— Tom doesn’t seem so enthusiastic as he was two years ago.
— Yes. He’s really reached a point in his career ______ he has to decide what to do next.
A．that
B．when
C．where
D．which
