右图显示，经济发展和环境质量之间的关系，根据这种关系，发展中国家应认识到（    ）

甲、乙两企业是谁违背了买卖合同？为什么？

                                                                              A Trip to the Forest
   One day Bob took two of his friends into the mountains. They put up their tents and then rode off to a forest to see how the trees were growing.
   In the afternoon when they were about ten kilometres from their camp（营地）, it started to snow. More and more snow fell. Soon Bob could hardly see his hands before his face. He could not find the road. Bob knew there were two roads. One road went to the camp, and the other went to his house. But all was white snow. Everything was the same. How could he take his friends back to the camp?
   Bob had an idea. The horses! Let the horses take them back! But what would happen if the horses took the road to his house? That would be a trip of thirty-five kilometres in such cold weather!
   It was getting late. They rode on and on. At last the horses stopped. Where were they? None of them could tell. John looked around. What was that under the tree? It was one of their tents!

写出下列单词的复数形式。

foot（复数）____

Ⅰ制备Fe₂O₃

【资料一】

①无水硫酸铜遇水变成蓝色的硫酸铜晶体．

②绿矾（FeSO₄•7H₂O）高温分解产生一种金属氧化物和几种气态非金属氧化物．

③SO₂是无色有窒息性臭味的有毒气体，能使品红溶液褪色．

甲同学用如下装置制备Fe₂O₃并验证绿矾受热分解的其他产物；