As time went by, the plan(which was) stuck to proved fairly practical.

参考译文：随着时间的推移，坚持的计划证明是很实用的。

A. to prove    B. to proved    C. to proving   D. to proves

解答如下：

B为正确答案。以上为过去分词作后置定语修饰前面的名词the plan , stuck to 为 遵守，坚持，谓语动词为proved，practical为表语。把省略部分还原为定语从句为“which was stuck to”先行词为“the plan”

stick to 为动词+介词构成短语动词，意思，坚持，遵守

特别备注：句中to为介词，是与前面动词stick构成stick to固定搭配。

状语从句：As time went by

主句：the plan(which was) stuck to proved fairly practical

主句语法结构分析如下

主句主语：the plan

修饰主语后置定语：(which was 省略) stuck to

主句系动词：proved

主句表语：fairly practical