已知P是数轴上的一个点，把P点向左移动3个单位后再向右移动1个单位，这时它表示的数是-4，则P点表示的数是（ ）。
-2
下列计算，正确的是[ ]
A.3+2ab=5ab
B.5xy-y=5x
C.-5m2n + 5nm2 =0
D.x3-x =x2
. My pain ___________ obvious the moment I walked into the room, for the first man I met asked me pitifully:" Are you feeling all right?"
A．must be
B．must have been
C．could be
D．could have been
