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（16分）人工合成的生长素类似物，如2.4—D、萘乙酸等，具有与生长素相似的生理效应。它们在生产上的应用很广泛。
(1)2，4—D 是一种最早应用的选择性除草剂，在农业生产上常用它除去单子叶农作物田间的双子叶杂草。单子叶农作物与双子叶杂草对2，4—D浓度的反应如右图曲线所示。

①从图中可以看出2.4—D作用的特点是_______________。
②图中X点（甲、乙的交点）对应的浓度对于双子叶杂草的作用效果是______________，2.4—D作为除草剂的最佳使用浓度是_______________点所对应的浓度。
③近几年，媒体经常报道有些农民使用除草剂导致作物绝产的消息。如是某农民使用的2。4—D不是假冒产品，请你分析导致作物绝产的最可能原因是__________________
(2)2.4—D还能促进插条生根。为了探索2.4—D促进插条生根的最适浓度，某生物兴趣小组先做了一组梯度比较大的预实验，实验的结果如下图所示。
①图中纵坐标的标识是______________；推测最适浓度的大致范围在______________之间。
②做预实验的目的是__________________ 正式实验中要实现实验目的，最少需要设置___________组实验（相对浓度梯度为1）。

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Most adults(成年人)once studied at school, had classes and did their homework every day. The same? ? ? is going on at school now. ??? ? it seems that doing weekend homework is ? ? problem for the modern students.

??? All the students should agree that weekend homework should be abolished(取消).It's??? ? for them studying at school five days a week. They have a lot of interests. With homework to do on Saturday and Sunday, when can they find?? ?? to help around the house, go and see a football or basketball game or a good film, join in family recreations（娱乐），or just have??? ? at home? Because of these other activities, the homework can't be finished until????? .So their weekend homework is usually done in such a hurry that on Monday teachers are????? and often threaten (威胁)to fail(使考试不及格)whole class of students because they know nothing about the??? . If there is no weekend homework for the students to do, they will be happy to go to school on Monday? ? having a good rest and to learn what the teachers teach.

1.A. thing??? ????????????? B. school ????????????? C. class??? ????????????? D. homework

2.A. Also??? ? ????????????? B. But??? ????????????? C. Still?? ????????????? D. Though

3.A. no??? ????????????? ????????????? B. another? ????????????? C. one??? ????????????? D. other

4.A. not enough????????????? B. enough? ????????????? C. no good? ????????????? D. no use

5.A. friends??? ????????????? B. time??? ????????????? C. places??? ????????????? D. money

6.A. a rest??? ????????????? B. an exam ????????????? C. a lesson?? ????????????? D. a picnic

7.A. Monday afternoon??? ????????????? ????????????? B. Saturday afternoon?

C. Friday night??? ????????????? ????????????? ????????????? D. Sunday night

8.A. pleased??? ????????????? B. sorry??? ????????????? C. unhappy?? D. not worried

9.A. lesson??? ????????????? B. games??? ????????????? C. interests? ????????????? D. activities

10.A. until??? ????????????? B. when??? ????????????? C. before?? ????????????? D. after

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Most adults(成年人)once studied at school, had classes and did their homework every day. The same is going on at school now. it seems that doing weekend homework is problem for the modern students.

All the students should agree that weekend homework should be abolished(取消).It's for them studying at school five days a week. They have a lot of interests. With homework to do on Saturday and Sunday, when can they find to help around the house, go and see a football or basketball game or a good film, join in family recreations（娱乐），or just have at home? Because of these other activities, the homework can't be finished until .So their weekend homework is usually done in such a hurry that on Monday teachers are and often threaten(威胁)to fail(使考试不及格)whole class of students because they know nothing about the . If there is no weekend homework for the students to do, they will be happy to go to school on Monday having a good rest and to learn what the teachers teach.

1.A. thing B. school C. class D. homework

2.A. Also B. But C. Still D. Though