modal. 必须;一定;应该;一定要;
n.必须做的事;
例句:
We must have the wall redone.
我们必须将那面墙重修一下.
The wicked must be wiped out.
恶人必须除掉.
Hospital operating instruments must be sanitary.
医院的手术器械必须是消过毒的.