部颁CDT规约一副帧结构由同步字、控制字和信息字组成，其中可以没有（）。
A.控制字
B.信息字
C.同步字
D.控制字和信息字
参考答案：B
There's a park _____ we can have a rest.[ ]
A. that
B. where
C. which
D. when
Was it from Libya ______ wars suddenly broke out _____ we managed to rescue the Chinese working staff?
A．that; where
B．which; that
C．where; that
D．where; which
