Health education cannot take the place of ______.

It cannot be used before ( )

A:inspect B:inspected C:being inspected D:inspecting

One cannot identify happiness with wealth．

Air pollution is caused by many things. Great clouds of smoke come from factories. Cars send smoke and fumes into the air. Burning waste fills the air with bits of dirt. Even burning leaves add smoke to the air. Sometimes, planes cannot find their landing spots through smoke. Smoke of all kinds is bad to breathe and can do great harm to the body.
Still, we cannot live without air. We must find a way to clean the air we have.
In time, we may have factories that are run by atomic energy. Our cars may run on smoke-free electric power. Scientists are also working on new ways to help the oil burned by cars from making fumes. Waste may be burned in the sand on ocean floors.
These changes might keep our air clean in the years to come. But until then, many scientists are looking for ways to make air cleaner now.
The story does not say so, but it makes you think that ______.

A:stopping air pollution is hard B:dirty air is blown away by the wind C:planes cannot fly through smoke D:it is impossible to make dirty air cleaner

Unfortunately, even computers cannot completelyerrors.

A:reduce B:diminish C:eliminate D:decrease

Which of the following CANNOT be taken on the plane?

A:chewing gum B:carry-on baggage C:weapons D:ammunition

"What cannot be found in the large scale charts? ________．

A:Radio beacons of small range B:Full details of all lights C:Elevations D:Full details of fog signals"

With the explosive popularity of mobile devices, we have witnessed a steady increase in demand for mobile date service. In addition mobile users also expect to connect to the Internet for communicate and access to services through the best suitable connection, anywhere and at anytime. Although the seamless roaming capability is well supported in conventional. Cellular communication networks, roaming and interworking technologies are still immature in heterogenous wireless networks. Seamless roaming over heterogenous wireless networks will be an ongoing and improved process, due to the requirements from both end users and network administrators. From the wireless access networks belonging to different administrative domains, mobile users cannot always identify at every instance which network is the best one to access for their service. It is highly demanded to establish a network architecture which can facilitate mobile terminals to access the appropriate network in a cost-effective way. If a mobile user wants to move from one network to another with continuous service, the terminals have to cope with network change to maintain service seamlessly. Quality of service is a major issue that the end users should be provided with the satisfying service, while the network workload and cost should not too much increased. In addition, since end users are provided with numerous service ranging from Voice-over-IP to Video-on-Demand services, it is expected that users can experience the same quality for all the different service. Therefore, the network architecture need to be designed in such a way that the quality mechanism is incorporated so that users are served according to their individual QoS requirements. Based on the paragraph above 。

Because of (　), mobile users cannot always identify at every instance which network is the best one to access for their services.

A:the different network administrative domains B:the same network administrative domains and mobile users C:mobile users D:the same network administrative domains