As time went by, the plan stuck fairly practical. A. to proveB. to provedC. to provingD.

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A. to prove
(答案→)B. to proved
C. to proving
D. to proves
解析：考查句子结构：本题为省略which/that的定语从句，stick to是“坚持”，宾语是省略的which/that。proved是the plan的谓语，句意：随着时间的推移，坚持的计划证明是很实用的。选B。