问题补充：
Having seen the X-ray, the doctor decided to the patient.
A. operate
B. operate on
C. work
D. work on
答案：
A. operate
(答案→)B. operate on
C. work
D. work on
解析：考查动词和动词短语：A．operate操作，经营，B. operate on给…做手术，C．work工作， D．work on从事，句意：看过X光后，医生决定给病人做手术。选B。
