Concept:When parallel lines are cut by a transversal, the alternate angles formed are equal.Explanation:Here, AB∥DE.Line BC acts as a transversal between the parallel lines AB and DE.From the diagram, ∠ABC and ∠CDE are alternate angles.Therefore, ∠ABC=∠CDE.The angle marked x is ∠CDE.Given ∠ABC=81∘, we get x=81∘.The value of ∠DCE=20∘ is not required to find x.Answer:x=81∘So, the correct option is C.