Which of the following is a first-order linear ODE?
y′+x2y=sin(x)y' + x^2y = \sin(x)y′+x2y=sin(x)
y′+y2=xy' + y^2 = xy′+y2=x
y′′+y=0y'' + y = 0y′′+y=0
y′=yy' = \sqrt{y}y′=y