Consider the following statements and select the correct answer using the codes given below: Assertion [A]: The length of the day at the equator is always 12 hours. Reason [R]: The angle of incidence of the Sun's rays at the equator is constant.

• 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.