Concept:Factorise by regrouping terms with a common factor, using c−a=−(a−c).Explanation:Observe that c−a=−(a−c). So rewrite the second term:x(a−c)+y(c−a)=x(a−c)−y(a−c).Now factor out the common factor (a−c):x(a−c)−y(a−c)=(a−c)(x−y).Thus, the expression simplifies directly to (a−c)(x−y).Answer:D. (a−c)(x−y)