A.x2ex B.ex C.xex D.(x+2)ex
A.12 B.13 C.14 D.15
A.c1y1+c2y2+y3 B.c1y1+c2y2-(c1+c3)y3 C.c1y1+c2y2-(1-c1-c2)y3 D.c1y1+c2y2+(1-c1-c2)y3
A.-1 B.0 C.1 D.2
A. B. C. D.