class Student(object):
    def __init__(self, name, score):
        self.name = name
        self.score = score

    def get_grade(self):
        if 60 <= self.score < 80:
            return 'B'        if 80 <= self.score <= 100:
            return 'A'        if self.score > 100 or self.score < 0:
            raise ValueError("% s 分数不合理" % self.score)
        else:
            return 'C'