四级翻译预测：

随着世界人口越来越密集(densely populated),空气污染已经成了严重的问题。空气污染主要来源于四个主要的人类活动领域：工业、能源业、交通运输业以及农业。经营工厂,为火车、飞机和公共汽车提供动力都需要能源。几乎所有这些能源都是通过燃烧燃料产生的,这就会造成空气污染。科学家们正在研究能减少环境破坏的新发电方式。增强的公共环保意识使诸如回收利用(recycling)等活动产生。

翻译范文：

As the world is getting more and more denselypopulated,air pollution has become a severeproblem.

Air pollution mainly derives from four majorhuman activity sectors:industry,energy,transportation andagriculture.

Energies are needed to run factories,to power trains,planes and buses.

Nearly all ofthese energies are produced by burning fuels,which would cause air pollution.

Scientists arestudying new ways of generating electricity that can be less damaging to the environment.

Theincreased public environmental awareness has led to the advent of activities such as recycling.

翻译详解：

1.随着世界人口越来越密集，污染已经成了严重的问题:“随着”可译为as,这句话可以用as引导的伴随状语从句来翻译。

2.科学家们正在研究能减少环境破坏的新发电方式:这个句子可翻译为包含定语从句的句子，new ways是先行词，引导词是that。其中“研究”可用动词study 表示;“发电”可译为generate electricity; “减少环境破坏”即“对环境的破坏更少”可译为be less damaging to the environment。