题目

 洋葱是生物学中常用的实验材料，下列相关叙述中正确的是( ) A. 洋葱的管状叶可用于观察叶绿体的形态和分布 B. 选用洋葱根尖分生区细胞可在光学显微镜下观察细胞中的基因突变学科... C. 紫色洋葱鳞片叶外表皮细胞可用来观察DNA和RNA在细胞中的分布 D. 紫色洋葱鳞片叶内表皮细胞是用来观察细胞质壁分离的最适材料之一 完形填空。      Many students talked about the rules that they have in school. At their school, they have to wear uniforms every day. The problem is that all the students think the uniforms are    1  . They think young people should look smart and so they would like to    2   their own clothes. Their teachers believe that ifthey did that, they would think more of their clothes than their    3  . But the students disagree. They would    4   more comfortable and that is good for studying. If they can't do that, they should be allowedto design their own uniforms. That would be a good way to keep both teachers and students happy. It's also probably a good idea for parents to allow teenagers to study in groups during the evening. Sometimes they get noisy    5   they can learn a lot from each other. They also think that vacations should be    6  . Atpresent they're too short. Longer vacations would give them time to do things like volunteering. Last summerthey had an    7   to volunteer at the local    8  , but they couldn't because they had to    9   to school. It would be a good experience   10   them because some of them want to be doctors when they grow up. (     )1. A. ugly      (     )2. A. put on     (     )3. A. clothes     (     )4. A. fall       (     )5. A. but       (     )6. A. shorter     (     )7. A. opportunity (     )8. A. school     (     )9. A. leave       (     )10. A. of          B. beautiful B. wear      B. study     B. fell       B. if        B. longer        B. chance          B. hospital  B. come      B. for        C. small     C. in     C. hair       C. feel     C. and     C. smaller        C. time      C. store   C. go back C. in       D. smart         D. do        D. shoes         D. felt        D. so         D. farther                        D. day          D. factory    D. live       D. with