【题目】No one knows when such a custom first _____.
A. came into power B. came into being
C. came true D. came out
在线课程【答案】B
【解析】
试题分析：考查短语。句意：没人知道这个风俗是什么时候形成的。A. came into power当权，上台，执政；B. came into being 形成；C. came true成为现实；D. came out出版；根据句意，风俗是形成的，故选B项。