构成自然景观地区差异的主要因素是（    ）

阅读下面短文，从短文后各题所给的四个选项（A、B、C和D）中选出最佳选项。

    Look at the car. It is Mr Black's car. It doesn't work now. Mr Black is under it. He is repairing it. Mrs Black is near the car. She is helping Mr Black. A girl is in the car. She is Kate, Mr Black's daughter. Who is the boy in the car? He is Jim, Kate's brother. It is Saturday today. They don't work. They want to go to Zhongshan Park. They all look worried.

已知A是无色无味的气体，B在A中燃烧更旺，生成无色气体C，C能使澄清石灰水变浑浊；D是空气成分之一，约占空气体积的4/5，将烧红的B放入C或D中立即熄灭，则：A是____；B是____；C是____；D是____。

写出B在A中燃烧的化学方程式____。