Growing up Micheal Jordan was in his prime, Beijing native Wu You knew what he wanted to

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A. since
(答案→)B. when
C. until
D. before
解析：句意：当乔丹在体育上的鼎盛时期时，地道的北京人吴悠正在慢慢地长大，他知道了他要做什么。since自从，既然；when当……时候；until到……为止；before
在……以前。根据句意故选B。