off the top of one's head
Jason：英语思维解密，为什么off the top of one's head指未经深思熟虑，轻松学英语
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off the top of one's head
off the top of one's head源自20世纪中期，指的是想法只来自大脑的表层。from the top of the brain不使用大脑的内部not using the inside of the brain。当你没有时间去思考、准备，可以用off the top of my head来给出你的答案。not off the top of my head即一时想不起来。
-How much do you think this car would be wotrh on a trade?-Well, right off the top of my head, I'd say about a thousand. -你认为这辆车可以卖多少钱？-嗯，我马上想到大约1000。
Off the top of my head, I couldn't tell you where they live, but I could soon find out. 想了想，我说不出他们住在哪里，但是我很快就能找到答案。
I cannot think of any good examples off the top of my head, but give me a couple of hours and I'm sure I could come up with something.我一时想不出什么好的例子，但是给我几个小时，我肯定能想出点儿什么来。