题目

Why doesn’t the unemployment rate ever reach zero? Economists, who generally believe that supply tends to meet demand, have long thought about this question. Even in good times, i.e. not now, there are people who can’t find work. And even in bad times, i.e. now, there are job openings. With over 14 million people out of work and looking for a job, you would think every available job would be filled. But that’s not the case. Not now and not ever. On Monday, the Nobel Prize committee awarded the prize for economics to the three scholars who have done the most to explain this phenomenon. Tw下图是叶片结构示意图,据图回答(方括号内填序号，横线上填结构名称，示例: (1)叶片由表皮、[ ]________、叶脉三部分组成。(2)植物进行光合作用的场所是细胞内的_________，通过光合作用产生的有机物通过叶脉中的_________(填植物的组织名称)运输到其他器官。(3)通过光合作用储存在有机物中的能量，要用于自身其它生命活动，需要通过_________作用才能释放出来，它的场所是细胞内的_________。