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

—We are worried about Tom. Why hasn’t he come back?—Don’t worry. He ______ in a traffic jam.

John, look at the time._____ you play the piano at such a late hour?

 — How’s your tour around the North Lake? Is it beautiful?— It ______ be, but it is now heavily polluted.

The school rules state that no child _____ out of the school, unless accompanied by an adult.