1. As it is getting close to the Spring Festival, the a_____________ in the street becomes more and more delightful.
2. At the same time we are taking measures to ___________ (保护)wild resources(资源).
3. A c__________ change takes place in any substance when it burns.
4. Many people are c___________ about the pollution of the _____________(环境).
5. I must post this letter at once; it's u___________.
