已知a+b=-5，ab=7，求a2+b2的值
∵a+b=-5，ab=7，
∴a2+b2=（a+b）2-2ab，
=（-5）2-2×7，
=11．
— What are the people like in mountain villages?
— I think they are _____ than those in cities. [ ]
A. friendly
B. friendlier
C. the most friendly
D. the friendliest
哪些用户不可办理IVPN业务（）
A.虚拟网用户
B.中继用户
C.NGN用户
D.普通直线用户
