题目

Working out can help teenagers boost their grades, a new study suggests. Adolescents who routinely engaged in moderate to vigorous（剧烈的）exercise showed long-term improvements in their academic performance, the British Journal of Sports Medicine study reported.“Our study suggests that the effect of physical activity may be quite large,” John Reilly, a professor at the University of Strathclyde said. The researchers looked at a sample of about 5000 children who were involved in a long-term study that tracks children born in the U.K. between 1991 and 1992. When children reached 11 ye甲、乙两种固体的溶解度曲线如图一所示，t2℃时，100 克水中加入 60 克硝酸钾，充分搅拌，直到固体完全消失，然后按图二进行实验，分别采用不同方法（每种方法只改变一个量），得到三个恰好饱和的溶液，且溶液质量依次减小。（1）t1℃时，溶解度大小关系为：甲_____乙（填“>”或“<”或“=”）。（2）t2℃时，配制 180 克甲物质的饱和溶液，需称量甲的质量_____g。（3）由图二推测硝酸钾是图一中的_____物质（填“甲”或“乙”）。（4）图二中“某一步操作”得到 E 杯中溶液的操作是_____。（5）图二中得到的 C、D、E 杯溶液中质量分数大小关系是_____（用“>或<或=”表示）。（6）图二中“某一步操作”得到D 杯溶液前后的溶液状态变化过程可以在图一中表示为_____（填字母序号）。A b 点→a 点 B c 点→a 点 C b 点→c 点 D c 点→d 点