Polluted air will seriously damage human health, affect crop growth and destroy ecological balance. Therefore, we should protect the air. In order to make the sky bluer, human beings are taking active actions, such as strengthening air quality monitoring, improving environmental conditions, using clean energy, and actively planting trees, flowers and grass to protect the air.
Therefore, the answer is to strengthen air quality monitoring, improve environmental conditions, use clean energy, and actively plant trees, flowers and grass to protect the air.