[求助]笨问几道语法题

poplar

大家好：

　　　小妹有好几道题不明白，请大家帮一下．

１．Ｐerhaps the most significant postwar trend was the decentralization of cities throughout the United States, ---------when massive highway-building programs permitted greater suburban growth.  a. and accelareated a phenomenon. b. a aphenomenon that accelerated. c. the acceleration of which phenomenon.  

which one is correct?  why?

2. ----------the percentage of individuals with similar traits in succeeding generations,geneticists use the theory of probability.  a. the calculation of.  b.  to  calculate.   c.  calulated.

which one is correct?  why?

3.the portrayal of everyday life in the objects of folk art makes it ---------- valuable source of history.  a. and .  b.  so that a.     c.    a

which one is correct?  why?      

thanks  a  lot!

happytoni

１Ｂ　　２Ｂ　３Ｃ

解释请看http://forum.chasedream.com/dispbbs.asp?boardID=58&ID=48503&page=1

poplar

thank you!