We must trace the source of these noxious gases.

我们必须查出毒气的来源。

youdao

He searched the grass and trees around the cotton fields to trace the source of the aphids.

他在棉花地周围的草丛、树干上找寻蚜虫产生的根源。

youdao

On Monday, they resorted to powdered bath salts to produce a milky color to help trace the source of the radiation leak.

星期一的时候，他们尝试着用沐浴盐所产生的白色气泡来判断核泄漏的地方。

youdao

But despite spills being "comparatively rare", he added that it would be difficult to trace the source.

BBC: Seabird deaths substance 'identified as oil substance'

Where the material originates outside the UK, the Internet Watch Foundation will attempt to trace the source and pass details to the National Criminal Intelligence Service.

BBC: NEWS | UK | Policing the net

After the first incident, the MCA launched an investigation into the spill, but has since said it had been unable to trace the source of the pollution.

BBC: More 'sticky substance' birds found in Devon and Cornwall