recognize:认出
realize:认识到,意识到
understand:明白
know：知道,认识
在句子中理
我知道答案,但我不明白,而且我没意识到我是错的：i knew the answer,but i didn't understand,and i didn't realize i was wrong.
我认识你,但我刚才没认出你来：i know you.but i didn't recognize you.