GWD一道语法题目，选项之间不是很不明白 求解答！！！谢谢大家！共同进步啊~~

joanna5200

Dolphins lack vocal cords, nevertheless creating sounds: a complicated system of whistles, Squeaks, moans, trills, and clicks are produced by sphincter muscles inside the blowhole.

• Anevertheless creating sounds: a complicated system of whistles, squeaks, moans, trills, and clicks are produced by
• Bnevertheless creating sounds: they produce a complicated system of whistles, squeaks, moans, trills, and clicks with
• Cbut they do create sounds, producing a complicated system of whistles, squeaks, moans, trills, and clicks with
• Dbut they do create sounds, a complicated system of whistles, squeaks, moans, trills, and clicks being produced
• Ebut nevertheless creating sounds: a complicated system of whistles, squeaks, moans, trills, and clicks produced by
  答案：C
• 我想问一下 D选项 错在哪里呢？？不是很明白呀？？求解答~~~快要考试了 ~谢谢大家~~
  

Ophena

D中a complicated system是sounds的同位语，但前者是单数，后者是复数，明显不一致。