The man in a black suit _______ be our youth worker.— I’m sure it _______ be him. I saw him in the laboratory building some minutes ago.

Look at my new digital camera. I bought it _____ June 1, Children’s Day.—Wow, how nice![ ]

It took him ____ to find the key to the drawer.

Leonardo da Vinci ________ birds kept in cages in order to have the pleasure of setting them free.

Having much to do，________．