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One day，our English teacher Mr．Smith came into the classroom with a book in his hand．He started his lesson with a question．"Who can（61） 　　what stress（压力） is like？"No one answered．Then he raised the book and asked，"How heavy is the book？"We（62） 　　to think and guess．One students stood up and said，"I think it is 100g．"Another student said，"It's 200g"Our answers were（63） 　　．At last，Mr．Smith explained．"It doesn't matter on the real weight．It depends on how long you hold it．If I hold it for a minute，it is OK．If I hold it for an hour，I will have a pain in my right arm．If I hold it for a（64） 　　，you will have to call a doctor．It is the extra same weight，but the longer I hold it，the（65） 　　it becomes．This book stands for stress．If you hold it without（66） 　　it down，sooner or later，you will not be（67） 　　to keep on．No matter how much stress you have，stop and have a rest for a while if possible．Boys and girls，you should learn to relax（68） 　　．I am sure you will live a happy school life．"We will never forget Mr．Smith and the meaningful（有意义的） lesson．

任务1：阅读短文（A），用方框中所给的词的适当形式填空，使文章通顺、连贯、合理．（每空一词，每个词限用一次）