下面哪种话单是PGW产生的？（）
A.SGW-CDR
B.PGW-CDR
C.S-CDR
D.P-CDR
参考答案：B
一How did you manage to succeed?
一It is only after we've lost everything __________we're free to do anything.
A．when
B．that
C．which
D．what
训诂
