读世界两大著名河流图，回答下题。

A．甲河在春季有积雪融水补给，并且存在凌汛。

B．甲河航运价值低，乙河的航运价值高

C．甲乙两河主要流经国家土地资源均很丰富。

D．甲河位于亚寒带针叶林带，乙河位于热带雨林带，两地森林资源都很丰富

Personal firewall is a technology that helps (57) intruders from accessing data on your PC via the Internet or another network, by keeping (58) data from entering or exiting your system.
Hackers do not just target national security organizations for (59) : They want your tax returns, network passwords, or bank account numbers. And you do not want the FBI kicking in your door because someone hijacked your PC to (60) in the latest denial-of-service attack on the Internet. Now that "always-on" broadband connections such as cable modems and digital subscriber line are becoming more popular, home users are at risk. Fortunately, you can protect your data. Firewalls can block (61) attacks and protect your PC from outside threats.

A. authorized B. refused C. deniedD. unauthorized