Given below are two statements,one labelled as Assertion (A) and other labelled as Reason (R):Assertion (A): Transformer is useful for stepping up or stepping down voltages.Reason (R): Transformer is a device used in D.C. circuits.

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is NOT the correct explanation of A
• C. A is true but R is false
• D. A is false but R is true