环境问题的实质是发展问题，对其含义理解正确的是

①没有人类社会及其发展，就没有当今意义的环境问题

②历史发展阶段不同，生产力水平、社会形态、人们的观念等都会不同，环境问题的性质、特点也会不同

③人类社会越是发展，环境问题越是严重。要解决环境问题，人类必须停止发展

④环境问题由人类社会发展而产生，也会因人类社会发展而得以治理 [     ]

A．①③④

B．②③④

C．①②④

D．①②③④

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. assignedB. does not justify C. replace D. does not replace