Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

Right now, the biggest source of energy in the world is fossil fuel. Fossil fuels are oil, gas, and coal. More than 80 percent of the world's energy comes from fossil fuel. There are many problems with fossil fuel. One problem is that when fossil fuel is burned, it pollutes the air. Also, when we take fossil fuel from the Earth, we often cause a lot of damage. Another problem is that we are running out of it. That is why we need new sources of energy. A big source of energy for many countries is nuclear power. Thirtyone countries use nuclear power. Many ships also use it.

Nuclear power has some advantages. First of all, we can’t run out of nuclear power. Nuclear power does not make the air dirty. Also, if a country has nuclear power, it doesn't need to buy as much as oil from other countries.



However, there are also a lot of problems that come with nuclear power. For example, nuclear accidentsare very serious. In 1986, there was a nuclear accident in Ukraine. In the next 20 years, about 4,000 people got sick and died. In 2011, there was another very serious nuclear accident in Japan. Japan is still trying to clean up the nuclear waste from the accident.

Many people don't want nuclear power in their countries. They say that it is not safe. A lot of people want their countries to use safer and cleaner ways to get electricity. There have been protests against nuclear energy in the United States, Russia, France, Taiwan, Japan, India, and many other countries.

Although many people hate nuclear energy, more and more countries are using it. One reason for this is that the world is using more and more energy. We just don't have enough fossil fuel. However, if we use nuclear power, then we may have more serious problems in the future.

The phrase "clean up" in paragraph 3 is closest in meaning to ___________