I hear that London is famous for the heavy fog. 我听说伦敦以浓雾而闻名。

Yes. London is a foggy city. 是的。伦敦是雾都。

Do you know why it is so foggy here? 你知道为什么这里会有浓雾吗?

It is because of air pullution. 是因为空气污染。

The air pollution in London has decreased. 伦敦的空气污染已经减轻了。

It is not so foggy like what we have expected. 这里并不像想象的那么多雾。

The air pollution in London has decreased. 伦敦的空气污染已经减轻了。

Why? 为什么?

The pollution in London decreased. 因为伦敦的污染减轻了。