—May I play computer games, Mum?—No, you ______. You’ve got a lot of homework to do. 

Don’t play with the dog, Jack, for it ______ be dangerous at times.

 -- Is it your brother playing football outside? -- It ________ be him. He is helping mother with dishes now.

No one ______ be more generous; he has a heart of gold.

— I phoned you yesterday morning. A girl answered, but I didn’t recognize the voice.— Oh, it __________ my younger sister. She was in my room at that moment.