Someone（must have been）here this morning.为什么括号里要这么填写

There must be someone living here[同义句转换]There must be someone ______ _____ here there must be someone in the room _(be)there 为什么不选D?I couldn’t get through.Someone ____ the telephone.A.B.略 C.must have been using D.must be using must be must have done 区别 must be,must和have be,have的区别 英语翻译Still needs financial information to be added to Acknowledgement section - someone must have paid for this work to be done. My watch is m___.Someone must have stole it Someone left the door of our classroom unlocked yesterday It ____Bruce.He was the last to leaveschoolAshould be B must be C must have been D should have been There must be someone around you______ _______ you can learn. our,neighborhood,visiting,there,be,someone,homes,the,in,must When someone says keeping smiling,he must be in There must be someone without possibility in their hearts. must be和must have be有什么区别谢谢 she___crazy to go out with someone like himcan be?may be?will be?must be? 是there must be someone can hear us还是there must someone who can hear us如果有不同, 初三同义句替换We have been waiting for many hours.We have been waiting ___ ___. There must be someone and he lives here.There must be someone ____ here. He spoke on TV that day.He ___ ____ ____ on TV that day. I won't let my parents d be have to是否等于must to must have been done/must be done求解两者异同