题目

It's important to learn how we can protect the environment. Here are 5R rules for us.Reduce. If you want to reduce waste, you should use things more wisely.【1】 If everyone uses paper carelessly, soon we would not have any trees left. Other things are also being wasted, and people don't know what to do with the waste in big cities. So it is necessary to reduce the amount of waste we produce.Reuse. You should always think of reusing things before throwing them out. For example,【2】. In a family, you may pass on such clothes to younger brothers or sisters.Recycle. Bottles, cans and paper c如图，在正方形ABCD中，E为AB边的中点，G、F分别为AD、BC边上的点．若AG=1，BF=2，∠GEF=90°，则GF的长为________．