cho các từ : must,can , should have, had to, needn"t, was able to, don"t have to, should, can"t, mustn"t, needn"t, must, ought, didn"t need to, can"t. 1 it is getting very late. we..... go home now. 1 I couldn"t go out last night because I........babysit for my sister. 3 you...........pay me back the money you owe me until next month. 4 " we ought to be getting ready now. "Yes, I guess we............" 5 we......... touch anything in this room until the police arrive. 6 It....be Helen. She has gone to Hanoi. 7 we need not do the washing up now. We ......do it tomorrow.