Thankfully the smoking of cigarettes is on the decline.

感谢的是吸烟正在减少。

His prosperity is on the decline.

他的好光景日见衰败。

Is your industry on the decline?

你所在行业是否正在下滑？

The birthrate is on the decline.

出生率在下降。

The population is on the decline.

人口正在减少。