realize:認識到，意識到
understand:明白
know：知道，認識
在句子中理解：
我知道答案，但我不明白，而且我沒意識到我是錯的：i knew the answer, but i didn't understand, and i didn't realize i was wrong.
我認識妳，但我剛才沒認出妳來：i know you. but i didn't recognize you.