An Integrating Factor for the Linear Differential Equation $x ^ { 2 } y ^ { \prime } + x y = 1$

Multiple Choice

An integrating factor for the linear differential equation $x ^ { 2 } y ^ { \prime } + x y = 1$ is

A) 0
B) 1
C) $x$
D) $1 / x$
E) $e ^ { x }$