Coal used to be a major source of fuel.

煤炭曾经是主要的燃料来源。

Rutile is a major source of titanium dioxide.

金红石是二氧化钛的主要来源。

The sun is a major source of radiative energy.

太阳是主要的辐射能量来源。

Petroleum is a major source of energy worldwide.

石油是全球主要的能源来源。

Vehicles are a major source of NOx in urban areas.

车辆是城市地区氮氧化物的主要来源。

Fossil fuels are a major source of greenhouse gases.

化石燃料是温室气体的主要来源。

Soybeans are a major source of protein for many people.

大豆是许多人主要的蛋白质来源。

Tourism is a major source of income for many countries.

旅游业是许多国家的重要收入来源。

Wastewater from factories is a major source of heavy metal pollution.

工厂排放的废水是重金属污染的主要来源之一。

The Jumna River is a major source of water for agriculture in the region.

朱木那河是该地区农业的主要水源。