One can’t do extreme sports he or she has had some training.A. ifB. unlessC. onceD. since

发布时间：2020-08-17 04:38:20

One can’t do extreme sports      he or she has had some training.
A. if
B. unless
C. once
D. since

网友回答

A. if
(答案→)B. unless
C. once
D. since
解析：句意：一个人不能做极限运动，除非他或她进行过一些培训。If如果； unless除非； once一旦； since自从，因为。根据句意故选B。
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