class Student(object):    def __init__(self, name, score):        self.name = name        self.score = score    def get_grade(self):        if self.score<0 or self.score>100:            raise ValueError('输入数值必须在0到100之间')        if self.score >=60 and self.score<80:            return 'B'        if self.score >= 80:            return 'A'        return 'C'