儿茶酚胺合成过程中的限速酶是（）

A.酪氨酸羟化酶

B.氨基转移酶

C.单胺氧化酶

D.多巴胺-β-羟化酶

E.丁酰胺酶

Personal firewall is a technology that helps______intruders from accessing data on your PCvia the Internet or another network, by keeping______data from entering or exiting your system.
Hackers do not just target national security organizations for______: They want your taxreturns, network passwords, or bank account numbers. And you do not want the FBI kicking in yourdoor because someone hijacked your PC to______in the latest denial-of-service attack on theInternet. Now that "always-on" broadband connections such as cable modems and digital subscriberline are becoming more popular, home users are at risk. Fortunately, you can protect your data.Firewalls can block______ attacks and protect your PC from outside threats.

A．attacks

B．aggression

C．help

D．repair