練習：把以下程式用函式重寫

grade.py

# 學生成績
student1_name = "Alice"
student1_score = 85
if student1_score >= 90:
    student1_grade = "A"
elif student1_score >= 80:
    student1_grade = "B"
elif student1_score >= 70:
    student1_grade = "C"
elif student1_score >= 60:
    student1_grade = "D"
else:
    student1_grade = "F"

student2_name = "Bob"
student2_score = 72
if student2_score >= 90:
    student2_grade = "A"
elif student2_score >= 80:
    student2_grade = "B"
elif student2_score >= 70:
    student2_grade = "C"
elif student2_score >= 60:
    student2_grade = "D"
else:
    student2_grade = "F"

student3_name = "Charlie"
student3_score = 67
if student3_score >= 90:
    student3_grade = "A"
elif student3_score >= 80:
    student3_grade = "B"
elif student3_score >= 70:
    student3_grade = "C"
elif student3_score >= 60:
    student3_grade = "D"
else:
    student3_grade = "F"

student4_name = "Diana"
student4_score = 93
if student4_score >= 90:
    student4_grade = "A"
elif student4_score >= 80:
    student4_grade = "B"
elif student4_score >= 70:
    student4_grade = "C"
elif student4_score >= 60:
    student4_grade = "D"
else:
    student4_grade = "F"

# 輸出結果
print("姓名：" + student1_name + '，等第：' + student1_grade)
print("姓名：" + student2_name + '，等第：' + student2_grade)
print("姓名：" + student3_name + '，等第：' + student3_grade)
print("姓名：" + student4_name + '，等第：' + student4_grade)