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）．

普罗塔戈拉曾说：“至于神，我既不能说他们存在，也不能说他们不存在，因为阻碍我认识这一点的事情很多，例如问题晦涩，人寿短促。”对此材料理解正确的是（    ）

阅读短文，掌握大意，然后从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。

    Last summer, my family and I went to England and we 1 two weeks in Cornwall. It 2 us five hours to get there by car. We stayed in a hotel near a lake. We did a lot of different   3  there: we went for long walks, played games, went shopping and swam in the lake.

    I played happily at first, but then  4 terrible happened. One morning I went to the  5  near the hotel by 6  . I walked and walked, watched the  7  singing in the trees and took some photos of them. When I got 8 , I wanted to go back to the hotel  9  food. But I couldn't find the way back. I  10  different ways. However, at last I was still in the 11 place.

    "Oh, God! What should I do? I'm so afraid!" I thought. Later it started to rain. I didn't have a(n) 12 so I was wet and cold.

    I  13  to stay under a tree and waited for my parents. After  14  hours they found me. It was dark and I was cold, hungry and scared. I will  15  go to the forest again.