利用条件运算符的嵌套来完成此题：学习成绩=90分的同学用A表示，60-89分之间的用B表示,60分以下的用C表示。

-Using a nested conditional operator to complete this question: academic = 90 points, said students with A ,60-89 minutes between the use of B said that 60 points or less with C said.