the centre is open from 9 to 8 Monday to Thursday and from 9 to 5 on Fridays during term time.
问题描述：
the centre is open from 9 to 8 Monday to Thursday and from 9 to 5 on Fridays during term time.
中为什么用FRIDAYS,而Monday to Thursday不加S?
答
ON FRIDAYS表示每星期五,这样的表示只能单独使用,也就是固定搭配
Monday to Thursday要表示每星期的话,只能是Monday to Thursday every week