He fell asleep immediately last night; he must ________ (be) very tired.
have been
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Somemoleculesarelargeenough________(see)undertheelectronicmicroscope.
Matteristhename________(give)toeverythingwhichhasweightandoccupiesspace.
Ifound________toanswerallthequestionswithinthetimegiven.
________(fail)severaltimes,theyneedsomeencouragement.
Onlywhenyouhaveobtainedsufficientdata________cometoasoundconclusion.
