一Tell us, Mark ,what is the ____ of the American Civil War?一 Well, is it because the black slaves wanted freedom?

He was faced with the    of whether or not to return to his country after he got the doctor's degree in America．

The plan was so shallow and impractical that no serious _________was ever made to realize it.

I didn’t know it could do terrible ______to your heart and lungs or ______was more difficult for smoking couples to become pregnant.

 His_______today made me angry . He should do things politely.