27.In 1929 relatively small declines in the market ruined many speculators having bought on margin; they had to sell, and their selling pushed other investors to the brink. (A) speculators having bought on margin; they had to sell, and (B) speculators who had bought on margin; having had to sell, (C) speculators who had bought on margin; they had to sell, and (D) speculators, those who had bought on margin; these speculators had to sell, and (E) speculators, who, having bought on margin and having to sell, D选项我觉得用了these speculators更好,不选它只是因为C选项的they指代无歧义而且更简洁吗?