People usually check whether their keys, purses and phones are with them before going out, but many people in China now have one more important thing to take, a mask (口罩). They hope it can protect them ____（1）__ terrible air.

   Many cities in China saw a lot of foggy days in April. In Beijing, there were eight days in April full of smog. It is dirty air ____  (1)  ____ looks like a mixture of fog and smoke. The smoke is mainly from cars and factories in cities. Poor air is bad for people's health, ____  (2)  ____ for children and old people. They fell ill easily and the ____  (3)  ___ were full of people. They had problems with their noses and lungs.

   So it's necessary ____  (4)  ____ people from doing so many bad things to the environment. For example, people should use cars less and ____  (5)  ____ burn lots of coal and gas. Government needs to take measures to make factories stop pouring ____（  (6)  ___ waste air into the sky.

   Three students from No. 4 High School in Beijing ____  (7)  ____ a report to advise how to protect the environment. They suggested ____  (8)  ____ people should plant more trees and set off fewer fireworks for celebration.

   We hope more people will join us in ____  (9)  ___ a difference. In this way, the blue sky will certainly return for good.