Read the passage carefully, then choose the correct answer.
Coal, oil, and natural gas supply modern civilization with most of its power. However, not only are supplies of these fuels limited, but they are a major source of pollution. Therefore, it's important to improve, explore and develop such alternative energy sources as nuclear, water, solar and wind power. Each of these alternatives, however, has advantages and disadvantages.
Nuclear power plants efficiently produce large amounts of electricity without polluting the atmosphere; however, they are costly to build and maintain, and they create the difficult problem of what to do with nuclear waste. Hydroelectric power is inexpensive and environmentally safe, but impractical for communities located far from moving water. Wind power is a pollution-free source of renewable energy but it cannot be used in many parts of the world where there is insufficient wind. Solar power is renewable, it does not cause pollution and it does not add the earth's heat load. However, it is difficult to collect and store. Solar power also requires expensive equipment.
Nuclear power plants________________.
A.are difficult to build
B.pollute the atmosphere
C.are very cheap to maintain
D.create the problem of nuclear waste

Các câu hỏi liên quan

Read the passage carefully, then choose the best answer for each question.
HAVE ALIENS VISITED US?
Many people have stories about seeing aliens. Here are two.
Judy Varns works for a group called the Mutual UFO Network. The purpose of this group is to research UFO sightings. Varns thinks a place called Area 51, in Nevada in the U.S., may be the best place on Earth to see UFOs. One day, she took some photos in the area and saw something she thinks is a UFO. "We saw this little disk-shaped thing in our photos. It's kind of exciting," she says.
Pat Travis lives near Area 51. One night, she saw a strange light in the sky. The light's movements were very unusual. Travis saw the lights move sideways and up and down. She saw them make many strange moves. Travis thinks it was a UFO.
Secrets of Area 51
Some people think Area 51 is where the U.S. Air Force keeps secrets, like UFOs that came to Earth and the aliens inside them. But really, Area 51 is a place the U.S. Air Force uses to test new technology, such as new kinds of aircraft.
James McGaha is a pilot who flew airplanes at Area 51. "There is absolutely no UFO activity at Area 51," he says. "No flying saucers, no live aliens, no dead aliens."So what did Varns and Travis see? Bill Fox worked at Area 51, too. He thinks he knows the answer. "We did build some strange-looking airplanes," he says. "I could see why some people would think they were UFOs."So are UFOs real? You'll have to decide for yourself. But if you do visit Nevada, keep your eyes on the skies!
Which of these sentences about Judy Varns is true?
A.She works at an airport in Area 51.
B.She helped Bill Fox build new airplanes.
C.She works as a pilot at Area 51.
D.She works for a group that studies UFO sightings.