---When were you born?---I was born______.
A. in1988 June 6
B. in June 6, on 1988
C. in June 6, 1988
D. on June 6, 1988
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We can see a big tree in______ front of the classroom building.
A. its
B. a
C. the
D. /
There is____ "s" in the word "us".
A. a
B. an
C. /
D. the
He likes playing______ football, but he doesn't like playing______ piano.
A. a, a
B. the, the
C. /, the
D. the, /
如线性规划的对偶问题无可行解,则原问题也一定无可行解。
A. 对
B. 错