The correct option is A Their end walls have perforated sieve plates which become impregnated with lignin at maturity
Sieve tubes are elongated tubular conducting channels of phloem. Each sieve tube is formed of several cells called sieve tube members, sieve tube cells or sieve elements. Sieve tube members are placed end to end.Their end walls have many small pores or sieve pits. Each sieve pore is lined by a layer of callose. Due to the presence of sieve pits, the end walls are commonly called sieve plates. A mature sieve element has a peripheral cytoplasm without nucleus. Structural proteins called P-proteins are present in the sieve tube elements.