81.尽管这两个运动员已经被警告过有危险，但是他们似乎都没把它当回事。
82.正是在一九四五年八月十五号，中国人民在抗日战争中取得了最后胜利。
83. Tom今年工作很努力，他赚的钱是去年的两倍。
84.虽然Black先生近几天背不公平地对待，但是他从未放弃希望。
85. 我室友说在晚上他不介意一直开着窗。
86. There are two possible explanations to account for the change in speed,but we don t know which one is right.
87. It was out of the question for Jim to finish the test paper within an hour because there were too many new words in it.
88. Scarcely had she put down the receiver when the telephone rang again.
89. He had been interested in history since his childhood, so he specialized in history when he was in college.
90. Our first acquaintance with them comes not from our mother s lips or from the talk of our classmates, but from books we read.
参考答案：
81.The two players had been warned of the danger, but neither of them seemed to take it seriously.
82.It was on August 15, 1945 that the Chinese people won the final victory in the Anti-Japanese War.
83. Tom has worked so hard this year that he will earn twice as much money as he did last year
84.Although he was unfairly treated those days, Mr. Black never gave up hope.
85. My roommate said he didn’t mind keeping the window open at night.
86. 有两个可能解释速度变化的原因，但是我们不知道哪个是正确的。
87. 对Jim来说，在一个小时内完成测试是不可能的，因为里面有太多的新单词。
88. 她刚放下电话，电话又响了。
89. 因为自从童年他就对历史很感兴趣，所以上大学时他主攻的历史专业。
90. 我们对他们的第一次相识不是来自我妈妈的嘴和同学的讨论，而是来自我们读的书。