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
A 有什么不对?为什么选c?
14. Several senior officials spoke to the press on condition that they not be named in the story. (A) that they not be named (B) that their names will not be used (C) that their names are not used (D) of not being named (E) they will not be named
177. Believed to originate from a small area on their foreheads, elephants emit low-frequency sounds that may be used as a secret language to communicate with other members of the herd.
(A) Believed to originate from a small area on their foreheads, elephants emit low-frequency sounds that may be used
(B) Elephants emit low-frequency sounds that are believed to originate from a small area on their foreheads, and they may use this
(C) Elephants emit low-frequency sounds, believed to originate from a small area on their foreheads, that they may use
(D) Originating, it is believed, from a small area on their foreheads; elephants emit low-frequency sounds they may use
(E) Originating, it is believed, from a small area on their foreheads, low-frequency sounds are emitted by elephants that may be used
The answer is (C)
Besides, to use "simple tense" seems at leaset as good as to use 完成时态 here, cuz this is a fact, no matter whether this creature is exist currently or not.