单项选择题

设p(x),q(x),f(x)均是x的连续函数,y1(x),y2(x),y3(x)是y"+p(x)y'+q(x)y=f(x)的3个线性无关的解,c1与c2是两个任意常数,则该非齐次方程的通解是 ( ).

A.c1y1+(c2+c1)y2+(1-c2)y3
B.(c1-c1)yl+(c2-1)y2+(1-c1)y3
C.(c1+c2)y1+(c1-c2)y2+(1-c1)y3
D.c(1y1+c2y2+(1-c1-c2)y3