A、a vacuum. B、full of dusts. C、full of atomic particles. D、windy. C

At one time, scientists thought the space between Earth and Sun was a vacuum. But we now know that the sun fills it with gusts of hot, electrically charged atomic particles called the solar wind. Sometimes this wind blows hard. When the Sun’s outer layer is very active, it hurls nearly one-third of its gaseous matter outward at supersonic speeds.
  The U. S. government’s oceans and atmosphere agency NOAA, has a Space Environment Center to monitor these discharges. The center’s director, Ernest Hildner, says intense solar emissions are not dangerous to people on the ground, but can be a hazard to airplane occupants and astronauts. They can also shut down satellites, power networks, communications, and other technical systems.