问题补充：
You will fall behind others you work hard.
A. if
B. unless
C. though
D. since
答案：
A. if
(答案→)B. unless
C. though
D. since
解析：A. if 假如 B. unless 除非 C. though 尽管 D. since自从；句意：除非你努力学习，否则你将落后与其他人。故选B
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