There are three separate sources of hazard【1】to the use of nuclear reaction to supply us with energy. Firstly, the radioactive m

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问题     There are three separate sources of hazard【1】to the use of nuclear reaction to supply us with energy. Firstly, the radioactive material must travel from its place of manufacture to the power station.【2】the power stations themselves are solidly built, the con-tainers used for transport of the material are not. Unfortunately, there are【3】only two methods of transport available,【4】road or rail, and both of these【5】close contact with the general public,【6】the routes are【7】to pass near, or even through,【8】populated areas.
    Secondly, there is a problem of wastes. All nuclear power stations produce wastes which【9】will remain radioactive for thousands of years. It is【10】to de-active these wastes, and so they must be stored【11】one of the ingenious but cumbersome ways that scientists have invented. For example, they must be buried under the ground【12】sunk in the sea. However, these【13】do not solve the problem completely, they merely store it, since an earth-quake could【14】open the containers like nuts.
    Thirdly, there is the problem of accidental exposure【15】to a leak or an explosion at the power station.【16】with the other two hazards, this is not very likely and does not provide a serious【17】to the nuclear program,【18】it can happen, as the inhabitants of Harrisburg will tell you.
    Separately and during short periods, these three types of risk are no great cause for concern. 【19】though, and especially【20】much longer periods, the probability of a disaster is extremely high.

选项 A、such as
B、for example
C、for instance
D、namely

答案D

解析 such as、for example和for instance都是部分举例,而此处是列出了所有可能的情形,namely意为“即,那就是”,正有此意。故正确答案为D。
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