1、-Have you finished your homework yet?

1、-Have you finished your homework yet?
-Not yet,I___to do it just a few minutes ago.
A.get down B.set out C.set about D.set up
（我感觉应该选C,可是答案给的B,为什么啊）
2、A new technique ___out,the yields increased by20％.
A.having working B.having been working
C.has worked D.had been worked
（答案给的B
3、____all the time is the key to____progress in English
A.Practice,making B.To practice,making
C.Practicing,make D.To practice,make
（答案给的B）