专四真题：求答案，求解析，一定要详细解析哦，谢谢了

Question

when I finish the story,Lenin jumped up from his chair and started pacing the floor______deep in thought.
A.with his head bending
B.in his head bent
C.his head bending
D.his head bent

Answer 1

原文是有逗号间隔开的：When I finish the story, Lenin jumped up from his chair and started pacing the floor, ____, deep in thought.
选 D)【句意】我讲完故事后，列宁从椅子上跳了起来，开始在屋子里踱来踱去,低着头，陷入沉思。【语法】 his head bent是独立主格结构，与谓语动词的动作同时发生，等于 and his head was bent。用逗号隔开时，就省掉了and 和was追问

省掉was?我还是不太懂，请问下这个地方bent是作形容词，弯曲的，还是作动词，但如果作动词的话，不应该是主动吗，was bent何解？我觉得是选A，也是独立主格，而且bending 是主动的

追答

我认为是当动词（被动）来解释，英文中“低头”是bend one's head,head做主语的话就要用被动head was bent ，要用with也是with his head bent；用bent弯曲的来形容头，不太合理