用适当的情态动词填空

you （）go and see a doctor at once because you 've got a fever.

the man in the office（）be Mr Black,because he went home just now.

may l go to the cinema,mum?certainly,but you （）be back by 11 o'clock.

who's that woman talking with Ann?l'm not sure.lt（）be her mother.

nobody （）live without air and water.