to choose完整的句子是i don't know which one i should choose.这时因为句子主语一致,可以省略后面的部分,就可以改写成i don't know which one to choose.这样的例子有很多,比如说what to do ,how to do 等等等等
to choose用to 不定式表目的翻译为:我不知道该选那一个
to choose在这里要用不定式 to do
to choose
to