Which of the following is not a property of double integration?

• A. af(x,y)ds = a f(x,y)ds, where a is a constant
• B. (f(x,y)+g(x,y))ds = f(x,y)ds+ g(x,y)ds
• C. ( _0^Df(x,y)ds = _0^{D1}f(x,y)ds+ _{D1}^{D2}f(x,y)ds, ) where D is union of disjoint domains D1 and D2
• D. (f(x,y)*g(x,y))ds = f(x,y)ds* g(x,y)ds