Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R) :
Assertion (A) : Sieve tube elements in phloem are living cells but lack nuclei at maturity.
Reason (R) : Companion cells control the metabolic activities of sieve tube elements through occluding junctions, ensuring the continuous pressure gradient necessary for phloem loading and unloading of sugars.
In light of the above statements, choose the most appropriate answer from the options given below :