填空题 (The age of) a geological sample can (be estimated) from the ratio of radioactive to nonradioaetive carbon (present) in the object (is examined). A. The age of B. be estimated C. present D. is examined
  • 1、
【正确答案】 1、D    
【答案解析】改为examined。过去分词短语在句中做定语，表完成和被动；the object examined被检测的物体。