Read the following passage and choose the best answer for each question.

Where will you go on your next vacation? Disneyland? Sea World? Outer space?

That’s right; tourists are now paying big bucks to travel into space with astronauts! The first space tourist was Dennis Tito, an American businessman. In 2001, he paid about $20 million to ride on a Russian rocket to the International Space Station. The Space Station circles 220 miles above Earth. Tito stayed on the station for a week, hanging out with astronauts and eating space food. The latest space tourist was Anousheh Ansari, an Iranian-born woman from the United States who went to the Space Station in mid-September 2006.

How safe is space travel? Apart from the risk of crashing, space tourists have some special things to worry about. Earth’s atmosphere protects us from dangerous radiation from the sun. Space travelers are exposed to more of the sun’s rays. But for tourists spending only a few days or weeks in space, the radiation probably isn’t harmful.

A bigger problem might be space sickness. Without Earth’s gravity to hold them down, visitors to the Space Station float around inside the craft. It may look like fun on TV, but it can make first-time space travelers dizzy and sick. Luckily, the sickness usually wears off quickly. Then space tourists can enjoy their trip and the amazing view of Earth.

It is probably so expensive to travel to space because_____.