1. The blizzard deposited more than a foot of snow on the train tracks, prompting the transit authority to shut down service temporarily and causing discontent among commuters who were left stranded for hours.
为什么and causing前面不加逗号？？
2. Tobacco companies, which have been shaken by a string of legal setbacks in the USA, but which retain strong growth prospects in the developing world, face an uncertain future.
but which前面的逗号可以省去吗？
第一个句子，promiting和causing平行并列，它不加逗号是因为要表达两个相同层次的并列关系，同时修饰第一句话，表达了暴风雪后雪大量沉积的两个结果，如果加逗号，会有歧义，causing是修饰前面的prompting那句话
第二个句子，which XXX, but which XXX,两个定语从句的并列，必须要有逗号连接，而且中间必须有连词，表示指代同一个名词，相同的结构有 which XXX, and which XXXX,如果没有逗号，容易认为第二个which修饰USA, 表达不是并列的含义
一家之言，仅供参考，希望能够帮助到你
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发表于 2017-12-4 20:45:55
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