that he isn’t adequate to the present job, he devotes all his spare time to studying professional knowledge.
A. Concern
B. To concern
C. Concerned
D. Concerning
网友回答
A. Concern
B. To concern
(答案→)C. Concerned
D. Concerning
解析：考查形容词做状语，concerned：对…担心，关心，是形容词做状语，表示状态。句意是：担心他不能适合现在的工作，他把所有的时间都用来学习专业知识。选C。