ITU-T的I系列建议共分6个部分，（）是关于ISDN的用户一网络接口.
A.I.100系列
B.I.400系列
C.I.600系列
参考答案：B
There has been an increase in the technical cooperation and cultural________ between China and
other countries in the past ten years.[ ]
A. change
B. trade
C. bargain
D. exchange
“发展才是硬道理”，只要经济发展了，其他问题都可以解决。
ncrease in the technical cooperation and cultural________ between China and