Maybe,"Oh, I see" 哈哈

Dear fdmaxey Thanks for your patient answer,that make me understand their meaning and how to use it, use chinese word say is “茅塞顿开”，这个词的意思是：一下子什么都明白了，但现在如果用英语来表达该怎么说呢？THANK YOU

There is no difference in meaning. They are interchangeable, except in one case: "No one of them knew the answer." This is correct. However, you could NOT say "Nobody of them knew the answer." You can't use 'nobody' followed by 'of'. There is some argument about which one is more formal. I have seen arguments both ways, so I wouldn't worry about it.