Concept:To factor the given equation, bring all terms to one side and take out the common factor.Explanation:Start with:x+y−ax=ay.Subtract ay from both sides:x+y−ax−ay=0.Group the x terms and the y terms:x(1−a)+y(1−a)=0.Factor out the common factor (1−a):(1−a)(x+y)=0.So the factorized form is (x+y)(1−a).Answer:C. (x+y)(1−a)