\eqalign{ & {\text{If }}a = \frac{x}{{x + y}}{\text{ and}} \cr & b = \frac{y}{{x - y}}{\text{, then}} \cr & \frac{{ab}}{{a + b}}\,{\text{is equal to = ?}} \cr} $$

• A. xy/(x2 + y2)
• B. (x2 + y2)/xy
• C. x/(x + y)
• D. (y/x + y)2