48. The golden crab of the Gulf of Mexico has not been fished commercially in great numbers, primarily on account of living at great depths-- 2,500 to 3,000 feet down. (A) on account of living (B) on account of their living (C) because it lives (D) because of living (E) being they live

OG explanation: As used in choices A, B, and D, the phrases on account of and because of are unidiomatic;because, which appears in C and E, is preferable here since because can introduce a complete subordinate clause explaining the reson why the golden crab has not been fished extensively.....Choice D, like A, fail to provide a noun or pronoun to perform the action of living, but even with its the phrease would e more awkward and less clear than it lives

问题1：why on account of and because of are unidiomatic

问题2：D和A中，living 的主语不可以直接看作主句主语么？谢谢

on account of 和 because of 都是介词, 介词必须跟名词. D和A中的living是分词, 而不是名词, 所以on account of living或者because of living 是错的.

living这个词单独用不一定就代表名次词性. 比如: Living at the top of the mountain, I enjoy the view very much. 此处Living表达的是一个动作. 如果前面加一个its, its living就变成一个名次性短语. 但即便这样og也解释说不如 because it lives来的好.