第四部分语法填空（共15小题，每小题1分，满分15分）
根据句子结构，在空格处填入一个适当的词语或使用括号中的词语的适当形式填空，并将答案填写在答题卷标号为51-65的相应位置上。
51. My younger sister is crazy __________ chocolate.
52. There was a time ______ he came to power and ruled the country with cruelty.
53. It was on the subway ________ the terriorists killed 20 people with the deadly gas.
54. He was recognized _______ a spy because of his heavy German accent.
55. He is the only person I can turn _______ for help when I am in need.
56. The river , _______ source is in Tibet, flows through 13 provinces in China.
57. Nelson Mandela , _______ played a leading part in helping balck people get the same rights as white people, is highly thought of all round the world.
58. The winter in 2008 was _______ (extreme) cold so that heavy snowstorms blocked the traffic in South China.
59. He offered _______ (guide) to poor black people on their legal problems.
60. Since the year 2000, the number of the students in Experimental School  _______ (reach) 3100, and our school is one of the biggest schools around Dongguan.
61. Though it was dangerous to go into that damaged building again, I persuaded him  _______ (rescue) the woman who was trapped under the ruins with me together.
62. After ________ (graduate) from college, we were determined to start our own business.
63. They heard the _________ (frighten) news and lost heart.
64. The train from Beijing _________ （arrive） at 5 pm and we will have enough time to meet him at the station.
65. They sent the _________ (injure) to hospital and buried the dead after the earthquake.