11. A significant proportions of the plants and animals of Hawaii exists nowhere

                       a                                b                  c

 else in the world.

              d

答案：  A

解析：  注意到句首的“a”,所以这里用单数形式，改为：proportion.

12. You will not be able to pass your examination except you study harder than you

                  a                                  b               c            

do now.

d

答案： B

解析： 表达“除非”的意思；except 改为unless。

13. Some bosses dislike to allow people to share their responsibilities; they keep

                          a              b

all important matters tightly in their own hands.

 c                       d

答案：  A

解析：  dislike doing sth. 指“不喜欢做…”。

14. Generally speaking, the bird flying across our path is observed, and the one

                                           a                               b

staying on the tree near at hand is passed by without noticed.

                             c                       d

答案：  D

解析：  without是介词，后面应该接名词或动名词，同时，该句又是被动的含义所以应改为:  without being noticed.

15. On the whole, ambitious students are much likely to succeed in their studies

          a                                b

than those with little ambition.

        c    d

答案：  B

解析：  此句是一个包含了比较级的句子，所以B项应改为： are more likely.