Concept:Use the distributive law to multiply each term of (2a−b) by each term of (a−b).Explanation:Expand using distribution: (2a−b)(a−b)=2a(a−b)−b(a−b).Multiply the first term: 2a×a=2a2 and 2a×(−b)=−2ab.Multiply the second term: −b×a=−ab and −b×(−b)=+b2.Add all the products: 2a2−2ab−ab+b2.Combine like terms: −2ab−ab=−3ab.So, the simplified expression is 2a2−3ab+b2.Answer:2a2−3ab+b2, which is Option D.