判断下列代码段的大O级别：
test = 0for i in range(n): test = test + 1for j in range(n): test = test - 1for k in range(n): test = test * 1
A、O(n)
B、O(n^2)
C、O(n^3)
D、O(n*log(n))
test = 0for i in range(n): test = test + 1for j in range(n): test = test - 1for k in range(n): test = test * 1
A、O(n)
B、O(n^2)
C、O(n^3)
D、O(n*log(n))