DNA的二级结构是A．β-折叠 B．α-螺旋 C．双螺旋结构 D．三叶草结构

下图为我国某地地质剖面图，读图完成下列各题。

（1）分析甲地地形形成原因。

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（2）丁地泥沙来源区的哪些气象灾害会加速该区域陆地面积变化？为什么？

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（3）请描述丙处地貌的形成过程和地貌特点。

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（4）简述④环节对河谷地貌形成的作用。

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词汇（10%）

小题1:The _           _(表现) of the students in class shows they like her.     

小题2:Children under 1.2 m in ___   __（高度） take the train freely in our country.

小题3:They looked at the car until it _         _(消失) in the darkness.        

小题4:He always _       _(鼓励) us when we failed in the exams.     

小题5:Miss Yang is a good teacher with lots of ___    ___（经验）in teaching.

小题6:I have come here s            to say hello to you.

小题7:The whole class waited a __________ for the results of the examination.

小题8:Have a little p___    ____， the bus will come soon.

小题9:It was reported that a plane crashed near the Indian Ocean, killing all the people on board, i____  _____ 56 passengers.

小题10:Your composition is good e___   ____ for some spelling mistakes.

长沙范围内有已探明的天然气资源吗？

在保税加工制度下，对境内企业进口的料件，只有由外商提供的，海关准予暂缓征收关税和进口环节税。 ( )

简述薄板换热器的特点。