He looked hard at the blackboard but could not ____(see) the word_英语解答

He looked hard at the blackboard but could not ____(see) the words clearly
如何确定是否是过去式,

人气：379 ℃　时间：2019-12-05 13:47:23

解答

see
looked 和 could 都是过去时的表现是不是该动作前头有过去式就可以原型。could，should都是对吗