he didn't come yesterday,he ______busy working in the lab怎么选must have been?.3Q

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hedidn''tcomeyesterday,he______busyworkinginthelab怎么选musthavebeen?.3Qhedidn''tcomeyesterday,he______bu

he didn't come yesterday,he ______busy working in the lab怎么选must have been?.3Q
he didn't come yesterday,he ______busy working in the lab
怎么选must have been?.3Q

he didn't come yesterday,he ______busy working in the lab怎么选must have been?.3Q
he didn't come yesterday,he __must have been____busy working in the lab
这里用的是过去完成进行时
他昨天没来,过去一直在工作

凡是情态动词 +have done 结构 必须所说的是过去的事 此题讲的是昨天的事符合条件
意思 昨天没来 必定是忙于做实验

意为“那时一定是...”
此句型用于表示对过去发生的事情的推测。