Michelle Obama wears clothes that anyone can buy in a mall and ________ she may have a larger effect on consumers than ordinary models.

---Fish need water to survive; _____ , we human beings rely on air to live.

He knows little of mathematics，______ of chemistry.

. Dream of the Red Chamber is _____ worth _____ because we can learn a lot about the noble families in the feudal society.

As is often pointed out, knowledge is a two-edged weapon which can be used ________ for good or evil．