Many young people don't work hard, and regret it later when the opportunity is gone.They only realize it________it is too late.
It is the bus driver who should ______ the safety of the passengers.
I’m very grateful to my high school teachers, without ______ help I wouldn’t be so excellent.
I ______ for Shanghai this Saturday, so I want to know when the earliest plane ______.
He ______ it on schedule, but somehow he fell behind.
The doctor’s dilemma was _____ he should tell the patient the truth.