Concept:To find the unknown expression, subtract the given expression from the target expression.Explanation:Let the required expression be P.Then (2x−3y)+P=x−2y.So, P=(x−2y)−(2x−3y).Remove brackets: P=x−2y−2x+3y.Collect like terms: P=x−2x+3y−2y.Simplify: P=−x+y=y−x.Answer:y−xTherefore, the correct option is B.