grade four的用法和樣例：
例句
- Hurricane Felix has been upgraded to a category four storm.
颶風費利克斯升至四級風暴。 - I suggest every province should also convene an all-province conference of cadres from three or four levels, with some from the co-operatives, to thrash out problems.
我建議各省也開一次全省性的三級或者四級幹部會議，摻一部分合作社的幹部，把問題扯清楚。
