—Which one of these two dictionaries do you advise me to buy, Oxford or Longman?

—Well, take Oxford. I think it is the ________ of the two.

A．best

B．better

C．good

D．well

一个数的分子扩大3倍，要使分数的大小不变，分母应（    ），这是运用分数的（    ）。