The correct option is D Sieve tube cell Phloem is composed of - sieve tube elements, companion cells, phloem parenchyma and phloem fibres.
Sieve tube elements are long, tube-like structures and are associated with companion cells. Their end walls are perforated to form the sieve plates. A mature sieve element possesses pheripheral cytoplasm and a large vacuole but lacks a nucleus. It becomes enucleate due to the degeneration of its nucleus during its developmental process.
The companion, parenchyma and meristematic cells possesses the nucleus throughout its life.