A group of students at Sunshine School are holding a charity sale to raise money to help their classmate Lisa. Lisa had cerebral palsy (大脑性瘫痪) when she was a baby. People who have cerebral palsy have trouble walking. Although Lisa has to use a wheelchair (轮椅) to help her get around, she never gives up.

    "Lisa has the chance of standing up, but she needs an operation (手术)," Lisa's doctor said.

    "I never thought that I could stand up one day. Actually the news is surprising for me. However, when I see my parents are worried about the cost of the operation, I am sad. I don't mind if I can't stand up," Lisa said. "Now my classmates and some other kind people are helping me. I am really thankful."

    "While helping Lisa, we can also learn a lot. We have learned how to cook cookies (曲奇饼) and how to sell them," Betty, one of Lisa's classmates said. "Now we know making money is not easy, so we won't waste money anymore."

    Alex, a boy in Lisa's class, told a reporter that they could raise about $100 every day. "We have raised about $2,100 so far. We hope we will raise more money for Lisa's operation," he said.

用锯末、废弃的玉米芯、菌苗，19天就能生产出珍稀杏鲍菇产品，而且供不应求，采摘后的废菌包再次变废为宝，变成含有大量有益茵群的高效多能生物有机肥和复混肥，农民使用后，可以增产增收……这种变废为宝的做法启示我们（  ）
①发展循环经济大有可为
②保护和改善环境也是保护和发展生产力
③我国的资源环境问题已经得到解决
④我国应该走生产发展、生活富裕、生态良好的文明发展之路

在关于x、y的方程组 中，当m为____时，这个方程组有无数个解．

根据汉语意思完成句子。