must will / must be going to

must will / must be going to must be going i must be to must will be 和will must be 哪个对 I am afraid I must be going at present,must to be. 为什么是must be kept而不是must to be kept 是must be to do还是must be doing You must be very excited about going to New York to study Look at the clouds,It ( )rain.A.will B.is going to C.must D. See the clouds!It() rain A.will B.is going to C.must D.may must be