【正确答案】正确答案：In sentence a, the thematic role of the door is theme.(2 points) In sentence b, the thematic role of the key is instrument, and the thematic role of the door is patient.(3 points) In sentence c, the thematic role of the boy is agent, that of the door is patient, and that of the key is instrument.(3 points)

【答案解析】解析：考查题元角色。题元角色主要是动词所表示的活动或事件中的相对恒定的参与者角色。在a句中，the door处于客体(theme)的角色；在b句中，the key处于工具(instrument)的角色，the door处于受事(patient)的角色；在c句中，the boy处于施事(agent)的角色，the key处于工具(instrument)的角色，the door处于受事(patient)的角色。