在毛细管中，表面张力可引起显著的液面（）。
A.只上升
B.只下降
C.无变化
D.上升或下降
参考答案：D
Only when his mother died ________ how much he loved his mother.
A．he realised
B．did he realise
C．he had realised
D．had he realised
挤压抛光有哪些特点？
