improve:promote,grow up,develop,enhance,reinforce,evolve...
as a matter of fact:actually,in fact,it is commonly accepted that,as a common sense that ,as we all know that...
nervous:tight,tense,anxious,embarrassed...
very fast:rapid,fleet,quick,swift,soon,before long,hurry up...
didn't:(这个没必要替换吧?)never
ahead of:before
how(这个也无需替换啊?)
difficult:hard,not easy,almost impossible...