What did he buy?好像对the...开头的划线提问，是用which 来开头。所以，用Which one did he buy? 或 which colour did he buy? 对不对？有道理！ which 所指是有一定范围的，从定冠词the 来看， 最好用which. 但毕竟one 也是提问部分。 我觉得应该是Which did he buy?刚才问个老师，她说，对宾语提问，用what, 对定语提问用which, 而本句是对整个宾语提问，所以要用what did he buy? 如果是对 定语 the red, 或red 提问，就用 which one did you buy? 您觉得如何？其它的同意， 由于宾语是特指的， 有一定范围，应该是whichWhich did he buy?