在夏至这天，假设温度相同而且都是晴天，则同种植物有机物积累最多的地区是（ ）
A．哈尔滨
B．北京
C．上海
D．海口
有机物的积累等于有机物的合成减去有机物的分解．植物的光合作用合成有机物，呼吸作用分解有机物．植物只有在有光的时候才进行光合作用，才合成有机物，虽然这时也有呼吸作用，但光合作用合成的有机物远大于呼吸作用分解的有机物，此时有机物是积累的，而无光的时候只有呼吸作用，分解有机物，有机物是消耗的．
夏至这一天，太阳直射点在北回归线．从四个地点的纬度来看，海口处在直射位置，辐照强度最大，但是植物体内有机物积累的多少主要因素不是光照强度，而是光照时间的长短．哈尔滨的纬度最高（太阳直射北回归线时，越往北日照时间越长，北极圈内会出现极昼现象），日照时间最长，因此哈尔滨的植物积累的有机物最多．
故选：A
阅读下面短文，根据所读内容在表格中的空白处填入恰当的单词。注意：每个空格只填一个单词。 Farmers and gardeners have long used greenhouses to extend the growing season in cold weather. Now, hoop houses are gaining popularity. Some hoop houses are rounded; others are shaped more like a traditional house. A hoop house is basically a metal frame covered with plastic or other all-weather material. A common design looks like a high tunnel. Unlike a greenhouse, which uses a heating system, a hoop house is heated by the warmth of the sun. Now, the United States Department of Agriculture has announced a program to help farmers who want to build hoop houses. The department has been supporting a project in Michigan. That state has a short growing season. As part of the research project, nine farmers were given materials and trained how to build and use a hoop house. The results showed that well-managed hoop houses can grow high-quality crops. However, crops are not the only things that grow well. The research found that weeds grow faster in a hoop house. Weeding (除草), seeding and watering requires at least as much work as crops grown in the open air. The researchers also advise growers to add compost（堆肥） material to the soil in hoop houses to build nutrients. Eliot Coleman is an organic farmer and a writer in Maine who has helped popularize the idea of four-season farming. His ideas about hoop houses sounded good to John Biernbaum in the Horticulture（园艺）Department at Michigan State University. Professor Biernbaum tried hoop houses on the Student Organic Farm at Michigan State and had success. Project director David Conner says it was a "test drive（试车）" for the research on private farms. The agricultural economist points to the demand for locally grown crops. "People are hungry for good, fresh vegetables," he says.
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