Which of the following declarations is incorrect in python language?

a$.$

xyzp $=5,000,000$

b$.$

x y z p $=5000600070008000$

c$.$

x$,$y$,$z$,$p $=5000,6000,7000,8000$

d$.$

x$\_$y$\_$z$\_$p $=5,000,000$