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                               bstaying 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                                bthan 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.