Holbrooke says the long-held notion that Afghanistan's illicit opium trade is the main source of funding for the insurgency is simply not true.

VOA: standard.2009.06.15

Glucose has to get into cells, that's the main source of energy source that cells use, metabolism of glucose.

但葡萄糖又必须进入细胞,因为它是细胞能量的主要来源,即通过葡萄糖代谢产生能量

耶鲁公开课 - 生物医学工程探索课程节选

So the main business of government consists in knowing how to control the elites because they are always a potential source of conflict and ambition.

因此统治的第一要务在于,懂得如何控制精英人物因为,他们往往是冲突和野心的潜在来源。

耶鲁公开课 - 政治哲学导论课程节选

(Speech) He says that today, the propaganda of arrogant nations of the world is the main source for the existence of conflict inside Iran.

VOA: standard.2009.12.07

In developing countries, the main source of water pollution is not stormwater,but waste water.

VOA: standard.2010.08.04