an eight hours' working day 错误。修改如下:
1 eight hours' working day
2 an eight-hour working day
至于为什么eight hours’ working day前为什么不能用不定冠词,语法书对此语焉不详。用惯用理解即可。WR网站对此有很多讨论的。又如:
Ten minutes’ walk
A ten-minute walk
A walk of ten minutes
但不能说 a ten minutes’ walk