I’m impressed with his determination. When he had a problem to solve, he _____ work at it until he found an answer.

That was a game. We were all at it.

How could I thank you enough? — Don’t mention it. Any other man ________ that. [ ]

doing market research, all the researchers think it ________ to spend a large sum of money on the project.

Who has broken the window in my room?— Who else ________ it but your naughty boy?[ ]