设线性无关函数y1、y2、y3都是二阶非齐次线性方程y″+P(x)y′+Q(x)y=f(x)的解,c1、c2是待定常数。则此方程的通解是:()
A:c1y1+c2y2+y3
B:c1y1+c2y2-(c1+c3)y3
C:c1y1+c2y2-(1-c1-c2)y3
D:c1y1+c2y2+(1-c1-c2)y3
出自:基础考试