关于大气颗粒物的来源和危害，下列不正确的是

A．可来源于自然界的风沙尘土、火山爆发
B．生产生活中的燃料燃烧可以产生颗粒物
C．在我国，颗粒物不是大气污染的主要污染物
D．颗粒物中PM₁₀占主要地位
E．颗粒物上可携带有毒物质

Even though current technologies make the ultimate segmented network impractical, new technologies and products hold the promise of making the concept a reality. Most important of all these new technologies are (71) . The ultimate switched LAN, which is technically possible, now, exhibits the following characteristics:
1. High-speed yet cost-effective switching devices can be implemented on a wide scale, providing dedicated connections for individual users and supporting the aggregate (72) of all networked users.
2. The ability to deploy switching capabilities incrementally into the (73) base. Switching implementations support switching of individual users or groups so that existing users of shared media modules can continue to use the existing equipment until they can justify moving to dedicate switched LAN connections.
3. Support and enhancement of existing routed environments. Switching (74) routint, but rather can be introduced into the network without making any changes to the existing routing equipment or configuration. (75) play a critical role in the integration of switching into existing networks.

A. specific requirementsB. bandwidth requirements
C. permanent requirementsD. security requirements