A.To express his doubts. |
B.To compare different ideas. |
C.To introduce points for discussion. |
D.To describe the conditions on Earth. |
A.Humans are nature-born to do so. |
B.Humans have the tendency to fight. |
C.Humans may find new sources of food. |
D.Humans don’t like to stay in the same place. |
A.Our genetic makeup. |
B.Resources on the earth. |
C.The adaptive ability of humans. |
D.By-products in space exploration. |