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问题 选择题

气孔是植物蒸腾失水和气体交换的“门户”，调节气孔张开和闭合的细胞是（　　）

A．上皮细胞

B．表皮细胞

C．叶肉细胞

D．保卫细胞

答案

我们把保卫细胞之间形成的凸透镜状的小孔称为气孔．

保卫细胞因腹侧较薄而背侧较厚，当吸水时，保卫细胞膨胀，两细胞分离，而气孔张开，保卫细胞失水时，气孔闭合．气孔在呼吸、蒸腾作用等气体的代谢中，成为空气和水蒸汽的通路，其通过量是由保卫细胞的开闭作用来调节，在生理上具有重要的意义，被称为植物蒸腾失水的“门户”，也是气体交换的“窗口”．

故选：D

选择题

For sustainable development, the government has decided to give ____ to those energy conserving and

environment-friendly business in many aspects. [ ]

A. profit

B. interest

C. advantage

D. preference

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完形填空

One night，at 1130 p．m.，an older African American woman was standing on the side of an Alabama highway trying to endure a lashing rainstorm.Her car had broken 小题1:______and she desperately needed a ride.Soaking (湿透) wet，she 小题2:______(decide) to flag down the next car.A young white man stopped 小题3:_____(help) her—generally unheard of in those conflict­filled 1960s.The man took her to 小题4:_____(safe)，helped her get assistance and put her into a taxicab.She seemed to be in a big hurry，but wrote down his address，thanked 小题5:_______.

Seven days went by and 小题6:_____knock came on the man’s door. 小题7:_____his surprise，a giant console color TV was delivered to his home.A special note was attached.It read，“Thank you so much 小题8:________assisting me on the highway the other night.The rain drenched (湿透) not only my clothes小题9:_______ my spirits.Then you came along.Because of you，I was able to make it to my 小题10:_______(die) husband’s bedside just before he passed away.God bless you for helping me and unselfishly serving others.”
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