专四真题：求答案，求解析，一定要详细解析哦，谢谢了

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