简述水稻品种南北相互引种后预期的效应。
参考答案：
在引种方面的应用纬度和海拔相近的地区，东西方向相互引种，因日长和温度条件相近，易于成功。北方的品种南引，因生育期间的日长变短，温度提高，品种的生育期缩短，往往生长量减少，不利产量形成。南种北引，因生育期间的日长变长，温度降低，品种的生育期延长，只要种植制度允许，能安全齐穗，即能发挥其增产潜力。高海拔品种引至低海拔，生育期的变化与北种南引相似；低海拔品种引至高海拔，与南种北引相似。
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| I always remembered the first time I took part in an English composition competition. "Right! Dean would be the __11__ of our class to participate in the English composition competition," my classmates said. I was too __12__ to speak when I heard what my classmates said. In order not to __13__ short of my classmates'__14__, I trained myself very hard for the hope of being the __15__ of the competition, which would take place a month later. I __16__ a lot of vocabulary, sentence structures and __17__ rules and read many good or renowned articles. Not having I __18__ pretty well, the day came. Every candidate __19__ me looked so wellprepared and __20__. "Only 1. 5 hours. Start," a supervisor suddenly said. Seeing the __21__ "What do most teenagers concern nowadays?" I was nervous and got __22__ block. What's worse, other candidates had begun writing. Moments later, I __23__ myself, took a deep breath, and began brainstorming ideas __24__ the topic. I quickly wrote down the composition structure, central theme, and __25__ necessary elements. As the finishing time was __26__, I tried my best to accelerate my writing. Unfortunately, __27__ my failure of time management, I left my composition incomplete. My final draft looked like a robot __28__ legs were broken. The result came out two weeks later. To my surprise, I got the second prize! All my classmates cheered for me. This encouraged me a lot. __29__ I was not the first prize winner, I could still __30__ pride and happiness spreading around me. | ||||
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