A father and his young daughter get on a bus and sit down. The conductor（售票员）comes to them for their money. The father says, "I want one ticket.”Then he gives the conductor some money. The conductor looks at the girl, then he asks, "How old are you?" The father starts to speak. But the conductor stops him, and the girl says, "I am six years old at home, and four years old in buses and trains. Father tells me that.’’ The father's face turns red. He has to take some money out of his bag and gives it to the conductor. The conductor gives him one and a half (半) tickets.

生态系统中碳循环的主要形式是（　　）

几乎快空心的柳树，树叶依旧繁茂，为了揭开树木不怕空心的原因？

第一步：查资料：植物体内有两种运输线，植物生活所需要的全部物质就靠这两种运输线来输送，一种是木质部里的运输线，另一种是韧皮部里面的运输线．它们分别运输水分和有机物等。

第二步：欲证明水分和无机盐是通过哪种运输线运输，设计了如下实验：

剪取生命活动旺盛的一根柳树（或月季）枝条，将柳树枝条基部纵剖，如图，下部处理成只有木质部（左）或只有韧皮部（右），分别插入两只烧杯的溶液中，烧杯中盛有红色土壤浸出液（红色物质对柳枝无害）．