Choose the correct option.

Some people in my class ... a lot of valuable resources that are difficult to ... . For example, some classmates always ... their packed lunches in silver paper which cannot be ... . Silver paper ... nature when it's ... into the environment because it ... very slowly. There are other, more environmentally friendly ways to ... food, and perhaps schools need to ... students to eliminate waste. As there are so many ways to protect the environment, people should ... ideas on their favorite ways. That way, we can ... the Earth clean.