A:The boy’s not having done
B:The boy not having done
C:The boy’s having not done
D:The boy having not done
凤兮凤兮!何德之衰?往者不可谏,来者犹可追。已而已而!____!
如图所示,在探究液体压强特点的过程中,将微小压强计的金属盒放在水中,下列做法能够使压强计u形管两边液面的高度差减小的是 ( )