用递归算法求1~n个连续自然数的乘积的代码如下,请选择合适的代码补全程序？（ ）
def Chengji(n):
if n <=1:
return 1
else:
return _____?______
print(Chengji(3))
n*Chengji(n)
n*Chengji(n-1)
n*Chengji(n+1)
n×Chengji(n-1)