【单选题】

There are three separate sources of hazard (21) to the use of nuclear reaction to sup ply us with energy. Firstly, the radioactive material must travel from its place of manufac ture to the power station. (22) the power stations themselves are solidly built, the con tainer used for transport of the material are not. Unfortunately , there are (23) only two methods of transport available, namely, road or rail, and both of these (24) close con tact with the general public, (25) the routes are (26) to pass near, or even through, crowdedly populated areas.

Secondly, there is a problem of wastes.All nuclear power stations produce wastes which (27) will remain radioactive for thousands of years. It is (28) to de-active these wastes, and so they must be stored (29) one of the ingenious but cumbersome ways that scientists have inventeD、For example, they must be buried under the ground or sunk in the seA、However, these (30) do not solve the problem completely, they merely store it, since an earthquake could (31) open the containers like nuts.
Thirdly, there is the problem of accidental exposure (32) to a leak or an explosion at the power station.Compared with the other two hazards, this is not very likely and does not provide a serious (33) to the nuclear program, (34) it can happen, as the inhabitants of Har risburg will tell you.
Separately, and during short periods, these three types of risk are no great cause for concern. Taken together, though, and especially (35) much longer periods, the proba bility of a disaster is extremely high.
A．means
B．ways
C．measures
D．methods