题目内容
The wreckage of something like a jet plain discovered in the heart of the desert is believed ______ a UFO and _______down for reasons still mysterious.
[ ]
A. to be; have fallen
B. to have been; to have fallen
C. to be; to fall
D. having been; having fallen
B. to have been; to have fallen
C. to be; to fall
D. having been; having fallen
A
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