单项选择题

设函数p(x),q(x),f(x)在区间(a,b)上连续,y1(x),y2(x),y3(x)是二阶线性微分方程y"+p(x)y'+q(x)y=f(x)的三个线性无关的解,c1,c2是两个任意常数,则该方程的通解是( )

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