885 section 4-23

23.   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

正确答案是C,我想问的是, it在这里指代会有歧义吗? 如果没有歧义的话那是不是就因为时态问题让C成为正确答案呢? 谢谢

请问是不是如果出现代词那肯定就是指带主句主语? 因为优先的话如果要指待别的话又不造成歧义,那就肯定不能用it 来指代了?

另外问一下,复合结构是怎么个定义的? and连接的句子？还是定语从句也算？