My father________hungry when he was young.

He is a very careful man, but he ________ make mistakes which seem ridiculous

 — What's the matter with the man hanging his head there?— Well, if you _____ know, he was caught stealing my bike. 

---Look at these tracks. It _____ be a wolf.”  ---Don’t be so sure. I think it _____ be a fox.

—Could I play computer games for a while, Mum? I’ve finished all my homework. —Oh, dear, if you _____.