He ________ to swim when he was five.

“No student,”the headteacher stressed, “_______ go out of the school after ten o’clock at night without my permission. ”

It was dark when Mary went out. I wonder how she ______ through the black lane by herself.

I’m going to Europe on vacation together with John if I _______ find the money.

— Is Mr. Smith driving here?  —I’m not sure. He ______ come by subway.