在下面一段文字横线处补写恰当的语句，使整段文字语意完整连贯，内容贴切，逻辑严密。每处不超过15个字。

    我国粮食已实现连续12年增产，与此同时，①____。为保障庞大人口日益增长的粮食需求，不能只靠进口粮食，而是要在水稻、小麦、玉米三大传统主粮之外，寻找到一种适合国情的新主粮。为此，②____。实际上我国已是全球马铃薯生产消费第一大国，但由于传统饮食消费习惯的影响和大众对马铃薯营养价值认识不够，③____。马铃薯具有易种植、产量高、营养丰、耐存储等特点，确可作为维系国内粮食供给的主粮。

20世纪50年代，欧洲的联合开始于（  ）

B

    I'm Sara. I'm a middle school student. At school, we have nine subjects — math, English, Chinese, science, geography, history, art, P.E. and music. My mother is a Chinese teacher and she says Chinese is beautiful and important (重要的). I like Chinese. I always read Chinese books before I go to bed. I also like history. It is my favorite subject. Mr. Brown is great fun. In his history class, I can learn many interesting stories.

    Mr. Green is my math teacher. He says math is useful and interesting, but I think it is boring. My science teacher, Mrs. Smith, is nice. I listen to (听) her carefully (认真的) in class. But I can't do well in the science exam(考试). I don't know why. This subject is really difficult for me.

    We always have art, P.E. or music in the afternoon. For me, the classes in the afternoon are fun and relaxing. In P.E. class, I like to play ping-pong with my P.E. teacher Mrs Miller plays very well.

根据材料内容简要回答下列问题

秦朝实行郡县制和隋唐时期的科举制度，在历史上发挥的共同作用是（    ）