There isn’t any difference between the two, I really don’t know ________．
A.where to chooseB.which to chooseC.to choose whatD.to choose which在线课程B
解析：
前面已经提到是两个，所以要用到which，表示从这两个里面选择;which to choose属于“疑问词+动词不定式”结构，这种结构经常在句子里面作主语、宾语和表语。