He fell asleep immediately last night; he must ________ (be) very tired.
have been
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Howlong________they________(dig)theditch?
Ishallneverforget________(meet)thelatePremierZhouduringhisinspectionofourfactory.
Tosucceedinascientificresearchproject________.
You________gonow.It’sgettinglate.
Ihavebeenstudyinghereforfouryears,bynextsummerI________.