下列程序的运行结果是？（ ）
L=[1,2,3,4,5,2,1]
L.pop(3)
L.pop(2)
print(L)
[1,2,4,5,1]
[1,2,3,5,2]
[1,2,5,2,1]
[1,2,3,5,1]
