Correct Option: D

Order is index of a derivative present in a PDE (i.e.) maximum there.

Hence,	δ2u	⇒ highest index 2 ⇒ order = 2
	δn2

if y, y₂ solution of a PDE, then PDE is linearly independent.

	δy1	+	y1δy1	=	δy12	......(1)
	δt		δx		δx2

	δy2	+	y2δy2	=	δ2y2	......(2)
	δt		δx		δx2

If y = ay₁ + a₁ y₂ is a sum of the PDE

	δ	(ay1 + a1y1) + (ay1 + a2y2)	δ	(ay1 + ay2) =	δ2	(ay1 + ay2)
	δt		d2		d22

Hence PDE is non linear of order 2