If (x+1)/(x-1)= a/b and (1-y)/(1+y) =b/a then the value of (x-y)/(1+xy) is :

• A. (a^2-b^
• B. /2ab2)(a^2+b^2)/2ab
• C. (a^2-b^2)/ab
• D. 2ab/(a^2-b^2 )