As we all know, Jack is experienced the problem of this kind.
A. to work out
B. at working
C. at working out
D. for working out
网友回答
A. to work out
B. at working
(答案→)C. at working out
D. for working out
解析：考查短语be experienced at在某方面有经验。At是介词后面接名词或者动名词。句意：众所周知，杰克在解决这方面的的难题上有经验。Work out解决，算出，故选A。