part of/a part of：
都表示部分，part of侧重不肯分割的部分及占比较大的部分，a part of侧重指较小部分 Right：Sleep is part of a person's daily activity cycle. Right：Our world is but a small part of the cosmos.
因果推理
P：afford a better view of the celebrities & do not stay as long as diners seated at standard-height tables
C：its profits would increase
若想削弱，就是反驳推理文段中的结论
因果推理
P：Once an airline successfully implements this method, any attempt to recoup the earlier losses by charging high fares on that route for an extended period would only provide competitors with a better opportunity to undercut the airline's fares.
C：this method of eliminating competition cannot be profitable in the long run
若问削弱，就是要反驳推理文段中的结论“this method cannot be profitable”
果因推理
P：in 1960 some polio vaccine was contaminated with the virus
C： this vaccine was the source of the virus found in mesotheliomas decades later
若想加强（取非），要么提到出现这个结果的另一个原因，要么讨论前提和结论中两件事儿的关系。
cells either do sth，in which case it is A, or do another thing, in which case it is B
cells either do sth，which made it A, or do another thing, in which case it is B,前句讲荷尔蒙使得细胞成为A，后句讲在前述事例里细胞是B，语意不够平行。
case可以指代整个句子，如：The sun ejects red fire, as is the case with any star of similar mass.
因此sb do sth,in which case……里，是case指代前面的句子，which修饰case，但没有指代句子。
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It purchases a company as a part of deal, as+宾语作状语修饰主句谓语动词purchase，意为将购买公司这件事情作为交易的一部分。
介宾短语不同于伴随状语，不需要以主句主语为逻辑主语。