臭氧层衰竭、酸雨和温室效应是当今世界三大环境问题．

（1）人为的大气污染物，使地球外层空间的臭氧层受到不同程度破坏，减弱了臭氧层吸收______的作用．

（2）形成酸雨的原因是空气受SO：和氮氧化物的污染．请举一例，说明酸雨可导致人类生存环境的恶化：

（3）形成温室效应的原因之一是______

你对防止温室效应的一点建议是______．

NAC，s rNetwork Access Control)role is to restrict network access to only compliant endpoints and (71) users．However，NAC is not a complete LAN (72) solution；additional proactive and (73) security measures must be implemented．Nevis is the first and only comprehensive LAN security solution thatcombines deeD security processing of every packet at 10Gbps，ensuring a high level of security plus applicationavailability and Derformance．Nevis integrates NAC as the first line of LAN security (74) ．In addition toNAC．enterFIrises need to implement role．based network access control as critical proactive security measuresreal．time，multilevel (75) inspection and microsecond threat containment

A．crisis
B．security
C．favorable
D．excellent