以下哪个程序段是使用递归函数实现1到100求和

A、def product1(num): product=1 for i in range(1,num+1): product=product *i return product print(product1(10))

B、def sum1(num): sum2=0 for i in range(1,num+1): sum2+=i return sum2 print(sum1(100))

C、def product2(num): if num==1: return 1 else: return num *product2(num-1) print(product2(10))

D、def sum_a(num1): if num1==1: return 1 else: return num1+sum_a(num1-1) print(sum_a(100))