因此，由于废气排放，它可能会造成严重的污染。

Therefore, it might cause a great deal of pollution because of ___exhaust fumes.

汽车废气是造成城市空气污染的重要因素。

Car ___exhaust fumes contribute significantly to urban air pollution.

现代发动机的设计旨在减少有害废气的排放。

Modern engines are designed to reduce harmful ___exhaust emissions.