在PDH信号接入SDH设备时需经过（）。
A.正码速调整
B.正/零/负码速调整
C.正码速调整或正/零/负码速调整
D.负码速调整
参考答案：C
Your mother looks a bit disappointed. You ______ have told her the truth. [ ]
A. should
B. must
C. can
短时记忆的特点是信息保持时间短，但容量无限。
