I would go with C.

The original sentence contains an error since "believed to be the largest flying creature the world has ever seen" is modifying the "wingspan of 36 feet," but obviously, the wingspan is not the the creature. From that, we can eliminate A, D, and E.

We can eliminate B because "and that is" is not parallel with "had a wingspan" and the "that" does not have a clear antecedent (the wingspan versus the Quetzalcoatlus).

We can choose C by process of elimination. It also has the correct tense, using "to have been" rather than "to be".

Please go through the explanation by scoobydooby.

https://www.beatthegmat.com/1000-sc-q8-t35056.html

Hope this helps

C is wrong because "it" is redundant. " to have been " is correct because infinitive is correct after a first verb and perfect present is correct to show a past action

in A, " belived to be" modify creature, not previous complete phrase. this case "believe to be" is consider "free modifier", which modify remote word, not attaching word. this is correct in general grammar books. "the word "free modifier" can be seen in general gammar books.

any idea, pls, tell me

I wish all of us discuss the official questions from good sourse. we should understand OA properly not only to know the right answer.

same topic going on at three different places and still we don't have any idea about OA...