问题
选择题
No one knows when such a custom first _____.
A．came into power
B．came into being
C．came true
D．came out
答案
答案：B
词义辨析。came into power掌权，上台；came into being 形成；came true 实现；came out出来，出版。句意：没有人知道这样的习俗最初是怎样形成的。所以选B。