off the top of your head
不加思考，直接回答或提出看法
口语·临时回答或猜测
英文释义
to give or provide an answer or response quickly, without taking the time to think or research
例句
I can't tell you the exact number off the top of my head, but I think it's around 50.
典故来源
源自20世纪早期，指信息像从头顶直接冒出一样，未经大脑深思熟虑。