The Differential Equation $\frac { \partial ^ { 2 } u } { \partial x ^ { 2 } } + \frac { \partial ^ { 2 } u } { \partial y ^ { 2 } } = 0$

Multiple Choice

The differential equation $\frac { \partial ^ { 2 } u } { \partial x ^ { 2 } } + \frac { \partial ^ { 2 } u } { \partial y ^ { 2 } } = 0$ is

A) first order, linear, homogeneous
B) first order, linear, non-homogeneous
C) second order, nonlinear
D) second order, linear, homogeneous
E) second order, linear, non-homogeneous