【In/at the back of one's mind】用来表达在脑海中挥之不去，或潜意识里担心某事,心事重重的感觉。例如， It's been in the back of my mind to call him for a couple of days. 这几天总想call他；It's always at the back of mind that the truth could be revealed.总是隐隐担心真相会暴露