I had been working on math for the whole afternoon and the n

had been working 过去完成时态 表明这个动作在过去的某个时段已经完成了 the numbers swam before my eyes一个过去式就ok了 其实swam就已经有过去的意思了 无论多久的过去.had swum感觉上说 已经眼花 什么的额 不好