A few years after World II finished, Scientists spoke with great eagerness about the use of nuclear  as source of energy. Within twenty years, they said, nuclear would take the place of coal, gas and oil as a source of power at home and in industry. This promise has never been carried out and there are serious doubts that it ever will be. Nuclear power plants are used to produce energy in some wealthier countries, but the cost is high. Although safety measures have been taken, radiation leaks  have taken place and workers have been killed or affected. The problem of getting rid of the nuclear waste has proved most difficult. There is a limit to the mount of waste materials which can be buried in the ground or poured in the seabed. These methods may also cause more problems. Waste materials polluted by radiation may remain dangerous for 200 years or more. It has no surprise that scientists have turned to the sun and the sea as sources of power. The sun shines day after day almost wastefully, providing us with energy far beyond all our earth. Nuclear waste must be dealt with carefully, because  _  .
It still gives off energy It's much more expensive than coal, gas and oil. It's harmful to people's health. It can burn easily.