An Assertion-Reason question of this kind is best resolved by first fixing the truth value of the Assertion and the Reason independently, and only then checking whether the Reason actually explains the Assertion, before testing each of the four composite options against that finding.
Testing all four composite claims shows that only the first one accurately captures both the truth of the two statements and the explanatory relationship between them.
Therefore, the correct answer is Both (A) and (R) are true, and (R) is the correct explanation of (A).