Consider the following statements and select the correct answer from the codes given below: Assertion [A]: The polar front theory states that masses of relatively, warm and cold air arc brought into contact. Reason [R]: These masses are known after their source regions.

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