DTE可以在（）虚电路区间发起呼叫
A、双向信道区间
B、永久虚电路区间
C、单向呼入信道区间
D、单向呼出信道区间
参考答案：A, D
—Look at the cloud! It looks like a rabbit.
—Wow. ______ beautiful!
A．what B. how a C. how
She had just finished her homework _____ hermother asked her to practise playing the piano yesterday. [ ]
A. when
B. while
C. after
D. since
