在国际企业价值链中，企业的增值活动可以分为上游环节和下游环节。下游环节增值活动的中心是（）
A.产品
B.客户
C.技术
D.市场
参考答案：B
句型转换.
1. Sally went to the pool yesterday. (改为一般疑问句并作肯定回答)
_____ Sally _____ to the pool yesterday?
Yes, she _____．
2. Did he study English well last year? (改为肯定句)
He _____ English well last year.
3. We did our homework last Friday. (改为否定句)
We _____ _____ our homework last Friday.
4. Her weekend was very interesting.(就画线部分提问)
_____ _____ her weekend?
5. I played soccer on my computer last weekend. (就画线部分提问)
What _____ you _____ on your computer last weekend?
【说明】
某公司的网络结构如图7.14所示，所有PC共享公网IP地址211.156.168.5接入Internet，另外有两台服务器提供Web服务和FTP服务，服务器的内网和公网地址如表7.7所示。
完成表7.9所示的防火墙上的NAT转换规则，以满足防火墙的部署要求。
