防火墙基本上分为哪两类：（）。
A、物理层和链路层
B、链路层和网络层
C、网络层和应用层
D、其它
参考答案：C
试述非小细胞肺癌的治疗原则。
This paragraph serves the consumer as ______.
A．important buying information
B．a challenge to buy more gold
C．a debate over gold prices
D．advice about buying silver
