尘埃量的增加一部分原因源于人类活动——比如，建筑，它属于直接原因，又如，为了耕种而将边际地块上的植物清除所造成的后果就属于间接原因。
Part of the increase stems from human activities—directly, in the case of construction, or indirectly, when it results from clearing vegetation from marginal land in order to farm it.
射猎活动源于人类最初的蛮荒时代。
大部分的沙尘暴都源于长期干旱，并由于诸如过度放牧和伐木等人类活动而更加恶化。
Most dust storms are linked to long droughts, exacerbated by human activities like overgrazing and deforestation.
它们源于人类活动最高尚的部分，都追求着深刻性、普遍性、永恒和富有意义。
They root from the most part of human being's activities, pursuing the nature of profundity, universalism, everlasting and full of meaning.
全球变暖的主要原因是人类的活动，温室气体像二氧化碳和氮氧化物，一些由工业企业排放的气体，能量来源于太阳能。
The major reason of global warming is due to human activities, the green house gases such as carbon dioxide and nitrogen oxides produced by the industry traps the energy from the sun.
全球变暖的主要原因是人类的活动，温室气体像二氧化碳和氮氧化物，一些由工业企业排放的气体，能量来源于太阳能。
The major reason of global warming is due to human activities, the green house gases such as carbon dioxide and nitrogen oxides produced by the industry traps the energy from the sun.
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