15.They failed six times but they have made their minds to t

15.They failed six times but they have made their minds to try _____.A.a seven time B.seven times
14.Smoking is so harmful to personal health that it kills ______ people each year than automobile accident.
A over six times B.six time
16.Which of them _____ something about the results that he doesn’t know?
A ,knows B.know C.knew D have know
17.The replacement of shops such as the grocers’ and chemist’s by cafes ____ the housewives with insufficient facilities for shopping.
B have left C has left
18.The first three of the five chapters in the book____ very easy,but the rest ____ difficult.
A.is ,are B are,are
19.The photos will show you___.
A.what does the house look like B.what the houses looks like.
C.how does the house look like D.how the house looks like
20.The air will be fresh and clean if we ____ rid of pollution.
A.will get B.will have got C.have got D.get
21.By the time you get to the Greenwich you ____ the most historic part of London.
A will see B are going to see C will be seeing D will have seen
14，b为什么不对？
15.They failed six times but they have made their minds to try _____.
A.a seven time B.seven times C.seventh time D.the seventh time
16.17.18 为什么?
19,d
20.c 21 d