<span>1050-1100 A.D. hope that helps !!</span>
They reveal that the ancient Chinese were good artisans!
Air pollution also can be cause by the Sierra madre Mt.
Explain it from a kids perspective, don't use big words and make sure to explain it so that it would be easy to understand what u mean. Go step by step. take it slow, and make it professional.
Hope I helped! ;)