python daily question每日一题 （#1）

欢迎来python每日一题来测试你对python基础知识的掌握 : ) ，问题都不难，不过大意或者对知识点模糊还是会出现错误~
Welcome to python daily question to consolidate the basics of python. Questions aren't complex but you may make mistakes.

下列哪个语句在python中是非法的，假设事先定义了x=0,y=0,z=0？
A. x = y = z = 1
B. x = (y = z + 1)
C. x, y = y, x
D. x += y

Which of the following statement is illegal in python, assume that x=0, y=0 , z=0first?
A. x = y = z = 1
B. x = (y = z + 1)
C. x, y = y, x
D. x += y