It is a good plan in theory, but it remains _______ whether it works in practice.
Rather than ___ on a crowded bus, he always prefers ___ a subway.
If you keep working so hard, I think you will succeed____.
He arrived at the station, ______that the bus_____ off .
Do you mind ____smoking here?
Jack doesn’t look ___ his father, but he walks ___ his father does.