A:HCl
B:Cl2
C:C2H2
D:CH4
(a,b)※(c,d)=(ac﹣bd,ad+bc),如(1,2)※(3,4)=(1×3﹣2×4,1×4+2×3)=(﹣5,10).若(x,y)※(1,﹣1)=(1,3),则xy的值是( )