【简答题】What is the main goal of sending human missions to Mars? A) To find out if life ever existed there. B) To see if humans could survive there. C) To prove the feasibility of large-scale space ventures. ...
【简答题】Something must be done to pr factories sending out poisonous gases so as to keep the city _________. A polluting B. from polluting C. pollute D. from being polluted