请教大全上一道题

tigerlioness

    

       
                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,（C）

    

(E) which is believed to be

          为什么选D?  B为什么不对呢？
          谢谢大家！

MangoQQ

看句子本身的意思, 是这一事实有到现在为止是世界上所见的最大的飞禽的意思，所以用现在完成时. 不知道解释的对不对.