A qualified doctor has to constantly update his knowledge in order to maintain his profess

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A. conscience
(答案→)B. petence
C. conservation
D. convenience
解析：A. conscience意识，B. petence能力，C. conservation保护，D. convenience便利，句意：一个合格的医生不得不不断的更新他的知识为了保持他的专业技能。选B。