They ______ going to school on foot before they went to high school.
The elderly _______ walking______.
My friend Anne is a _______ girl, and she has a lot of imagination and new ideas.
—He’s never heard to sing a pop song so loudly, ______ he?—______. He is so shy.
We believe scientists will ______ a way to solve the problem of air pollution.
The window was broken. Try to ______ who has broken it.