But variables like pedestrians in crosswalks, large crowds and vehicle wrecks can throw a carefully designed system out of whack, leading to annoying and pollution-causing traffic jams.

但是，正在穿越人行横道的路人、摩肩接踵的人群以及道路上抛锚的事故车等不确定因素都可能让一套精心设计的系统崩溃失常，导致恼人而又产生污染的交通拥堵。

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China Daily reports that more than 5, 000 tons of highly toxic industrial waste were dumped illegally in rural areas in Yunnan province, causing livestock deaths and soil and water pollution.

据《中国日报》报道，5000多吨剧毒化工废料在云南省的农村地区被非法倾倒，造成家畜死亡、土壤水源污染。

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Third, pollution from trucks and smoke covers glaciers with carbon soot so that their surfaces become darker and less reflective - causing them to melt more quickly.

第三，汽车尾气污染和烟雾使冰川被碳烟灰所笼罩，从而使冰川颜色变得更深而缺乏反射性——因而导致冰川加速融化。

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But when it comes to reducing pollution-causing emissions, electric vehicles have a lot of competition from cars powered by natural gas.

CNN: Natural gas vehicles on a roll in U.S.

The EPA last year issued the first-ever standards to control smog- and soot-forming gases from gas wells site, and updated existing rules to reduce cancer-causing pollution, such as benzene, from other equipment.

NPR: Report: Flaws In EPA Drilling Pollution Data

Opponents warn that fracking is an environmental disaster waiting to happen, citing, among other risks, air and water pollution, the release of radiation and cancer-causing substances, and the acceleration of global climate change as methane and other greenhouse gases escape during fracking.

FORBES: Fracking: A Role for Universities