阅读下面材料，在空白处填入适当的内容（不多于3个单词）或括号内单词的正确形式。

For many years, volunteers, both young and old, have been helping the poor and elderly people of this area. They work long hours building wheelchair paths, fixing leaky(有漏洞的) roofs and repairing the homes of those____ need help. Their only payment is the happy smiles and grateful hearts of the people whom____have helped.

I will always remember one man in particular____he has a real enthusiasm for voluntary work. He seemed to have inspired all the people in his group with his____(cheer) spirit. Every day when I asked him____he was doing, he would reply, “I'm doing good!”____the end of the month as he was preparing to leave, I looked at all the homes he ____(fix) and had to agree that he was indeed doing____good job!

A nice house, a successful career, and a lot of money might be nice to have, but____(compare) with fixing others' home and helping those who are in need, their____(significant) is not so great.

 材料一：钓鱼岛是我国固有领土，其附近海底蕴藏着丰富的可燃冰．可燃冰主要含有甲烷水合物，还含有氮气、氧气、二氧化碳、硫化氢和稀有气体等．

材料二：钓鱼岛附近海域是我国东海渔场，蕴藏着丰富的海产品，这些可食用的海产品为人类提供丰富的蛋白质和磷、钙、铁、锌、碘等元素．

根据上述材料，请回答：

（1）写出可燃冰成分中任意一种单质的化学式____ ；

（2）目前，可燃冰开采技术还不成熟，如果开采过程中____大量泄漏于大气中，将比二氧化碳造成的温室效应更严重；

（3）我国渔民捕获的可食用的海产品中，能补充人体所需要的____ 等微量元素（写一种元素名称或符号即可）．