mobile source of pollution

例句：

1. 1. The mobilesource of pollution is a major concern forenvironmentalists.
   移动污染源是环保人士的主要关注点。
2. 2. The mobile source of pollution isoften more difficult to control than stationarysources.
   移动污染源通常比固定源更难控制。
3. 3. The mobile source of pollution is agrowing problem in many cities around the world.
   移动污染源是全球许多城市日益严重的问题。