A number of harmful substances have been found in the air there.
那些地方的空气中已发现一些有害物质。
The main cause of pollution is the release of harmful substances into the environment.
污染的主要原因是将有害物质排放到自然环境中。
The main cause of pollution is the release of harmful substances into the environment.
污染的主要原因是将有害物质排放到自然环境中。
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