单项选择题
A.X1+X2+X3B.X1+X3+X2X1/X1C.X2+X3+X2X3/X2D.X1+X2+X1X2/X3
A.0B.1C.2D.3
A.ΔU%U2/100SeB.ΔU%100/U2SeC.100Se/ΔU%U2D.100U2/ΔU%Se