ninety/ninth

ninety /ˈnainti/ I. num.九十；九十岁：The old man lived to the age of ninety. 那老人活到九十岁。‖II. n. (pl.nineties) 90年代；90来岁：in the nineteen nineties在二十世纪90年代She was well into her nineties when she died. 她死的时候已经90好几了。

 ninth /nainθ/ num.第九，九分之一：One-ninth of the students come from Beijing. 九分之一的学生来自北京。The ninth lesson is too difficult for us.第九课对我们来说太难了。