Assertion: Nitrogen-fixing enzyme in legume root nodules function at low oxygen concentration.

Reason: Low oxygen concentration is provided by leghaemoglobin.

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

(c) If the Assertion is correct but Reason is incorrect.

(d) If both the Assertion and Reason are incorrect.

(e) If the Assertion is incorrect but the Reason is correct.