A．Someday human beings will be able to live on a spaceship.B．Space travel will cause pollution to other planets.C．Man must stop abusing the environment in order to have a better future.D．The spaceship Earth can not make a trip to the moon when its supplies are used up.
A．Someday human beings will be able to live on a spaceship.
B．Space travel will cause pollution to other planets.
C．Man must stop abusing the environment in order to have a better future.
D．The spaceship Earth can not make a trip to the moon when its supplies are used up.