those gril's are,those are office?

those gril's are,those are office?
those grils are very lazy.
those are office assistants.
从语法上讲哪句是错的?为什么?
其实2个句子都是对的。只是我不清楚those grils are very lazy和those are grils very lazy有什么原理区别，those are grils very lazy不是和those are office assistants一样吗？但是课本说我的those are grils very lazy是错的。