Both his parents look sad. Maybe they_______ what's happened to him.
A. knew
B. have known
C. know
D. will know
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Hardly _________ our walk when it began to rain.
A. we began
B. we had begun
C. had we begun
D. has we begun
I was walking along the street _________ I met an old friend.
A. that
B. which
C. while
D. when
He ______ school last year. Now he earns his living as a worker.
A. leaves
B. has left
C. left
D. had left
By the time he ______ to the station, the train _____.
A. go; have left
B. went; have left
C. had come; left
D. went; had left