“what can they be doing”

“what can they be doing” What can they be的意思 What are they doing? what are they doing What do they doing? 英语what are they doing what are they doing?急用! What do they like doing? what are they doing now? They are--- the doctors are busy doing what they can to save dying man,这 The doctors are busy doing what they can _____ the dying man The teachers are doing what they _____ their stuaits.A.can t