新概念。   

   I have just    1   a letter from my brother, Tim. He is in Australia. He has been there for six    2   . Tim is an    3   . He is working for a big    4   and he has already visited a great number of    5   places in

Australia. He has just    6   an Australian can and has      7   to Alice Springs, a small town in the    8   of

Australia. He will soon visit Darwin. From there, he will    9   to Perth. My brother has never been    10  

before, so he is finding this trip very exciting.

最新的研究和统计表明，安全攻击主要来自（）。

A.接入网

B.企业内部网

C.公用IP网

D.个人网