请教蓝皮316页110题

A huge flying reptile that died out with the dinosaurs some 65 million years ago, the Quetzalcoatlus had a wingspan of 36 feet, believed to be the largest flying creature the world has ever seen.

(A) believed to be
(B) and that is believed to be
(C) and it is believed to have been
(D) which was, it is believed,
(E) which is believed to be

蓝皮上的一道题，答案是C，不懂啊，望高人指教！

上XDF的时候老师说，遇到world has ever seen，就用完成时

具体原因我也不懂

which就近修饰wingspan，与后面的句子内容不符，排除de

and that没有并列对象

believed to be 分词就近修饰前行名词wingspan，不合逻辑

我觉得这句话的结构是：同位语从句，句子1，and 句子2。