81. 我经常遗憾在我年轻的时候没有好好学习。
82. 那个老妪一打开大门她的狗就跑出了院子。
83. 晚上直到他写完作业他妈妈才允许他看电视。
84. 男生们花了一早上来讨论问题的答案。
85. 据报道，到上个月结束，公司的销售已经提高了百分之十。
86. If there is no one to help him with the preparation，he will have to put off the meeting
87. As soon as she tears open the letter，Mrs. White will find out what has happened to her Husband
88. Unless the government agrees to give extra money，the theatre will have to be closed next month.
89. You couldn t have seen Jane in her office last Friday，for she s been out of town for two weeks.
90. Scientists have searched for many years for a method to tell whether a volcano explosion will be small or large.
参考答案：
81. I always regret not studying harder when I was young.
82. Her dog ran out of the yard as soon as the old lady opened the gate.
83.Not until he finished his homework did his mother allow him to watch TV in the evening.
84. The boys spent the whole morning discussing possible answers to the question
85. It s reported that by the end of last month the sale of the company had risen by 10%.
86. 如果没有人帮他准备，他将会把会议推迟。
87. 怀特夫人一撕开信，她就明白了她丈夫发生了什么。
88. 除非政府同意给额外的钱，否则下个月剧院将被迫倒闭。
89. 上周五你不可能在简的办公室看到她，因为她已经去乡下两周了。
90. 为了辨别火山爆发是大还是小，科学家已经做了许多年的研究。