先来一个例子: 24. Just as plant species native to regions with browsing mammals evolved many natural anti-browser defenses (such as sharp spines and toxic chemicals), so humans in malarial regions have evolved dozens of chemical defenses against malaria. (A) so humans in malarial regions have evolved dozens of chemical defenses against malaria (B) humans in malarial regions have been evolving dozens of chemical defenses against malaria (C) there has been, in malarial regions, an evolution of dozens of human chemical defenses against malaria (D) dozens of chemical defenses against malaria have been evolved by humans in malarial regions (E) similarly, in malarial regions, humans have evolved dozens of chemical defenses against malaria 答案:A
[此贴子已经被作者于2003-9-29 22:21:27编辑过] |