In which of the following differential equation degree is not defined? (a)`(d^2y)/(dx^2)+3(dy/dx)^2=xlog((d^2y)/(dx^2))` (b)`((d^2y)/(dx^2))^2+(dy/dx)^2=xsin((d^2y)/(dx^2))` (c)`x=sin((dy/dx)-2y),|x|<1` (d)`x-2y=log(dy/dx)`