小行星是否是人类外太空迁移的好选择。

Refute the three explanations mentioned in reading passage.
1. The lecturer refutes the point by saying that there lie many risks, for the muscle and bones will suffer if people are under the low gravity for a long time.
2. It causes a large amount of additional costs to obtain the metals. Because transporting the metals to the earth costs much, and people cannot guarantee what they unearth is just the metal they expect.
3. The asteroid’s orbit is not regular, so when it

Sending people to asteroids for colonization is optional.
1. Low gravity in the asteroids contributes to taking off and landing safely, as well as consuming less fuel.
2. People can mine valuable and rare metals from the asteroids, thus they can gain many more profits.
3. It is easy to reach the asteroid which is near the earth.