All the following statements regarding sieve tube elements are correct except that:

• A. their end walls have perforated sieve plates which become impregnated with lignin at maturity.
• B. they possess peripheral cytoplasm as well as a large vacuole.
• C. distinct proteinaceous inclusions, the P-proteins are seen evenly distributed throughout the lumen.
• D. long, slender, tube-like structures arranged in longitudinal series.