以下代码实现了根据分数返回等级（A:90-100,B:80-89,C:70-79,D:60-69,F:0-59）的功能，请选择正确的选项填入①②处。
grade_map = {90: "A", 80: "B", 70: "C", 60: "D", 0: "F"}
def get_grade(score):
if score < 0> 100:
return "无效分数"
for key in sorted(grade_map.keys(), reverse=True):
if score >= key:
return ___①___
score = int(input())
grade = get_grade(score)
print(f"分数 {score} 的等级是 {___②___}")
