SDH的主要优点是
A.同步复用
B.标准网络接口
C.强大的网络管理
D.以上都是
参考答案:D
解析:【解析】SDH的主要优点有同步复用、标准光接口和强大的网络管理。
The Acropolis ________ in the 5th century B. C. at a high altitude above the city in honour of
Athena, the goddess of Athens.[ ]
A. constructed
B. was constructed
C. has been constructed
D. is being constructed
Mike has much difficulty ________ Chinese so he often asks me ________ help.
A.to understand, with
B.understanding, of
C.to understand, for
D.understanding, for