雷云对地放电过程中、主放电持续时间约（）us。
A.30一40
B.40一50
C.50-100
D.>100
参考答案：C
下面哪个是思科公司推出的认证考试（）
A.orical
B.HCSE
C.CCNA
D.CIW
The process whereby software is installed into an operational environment is called "______".
A．deployment
B．development
C．setup
D．lay up
