. The reason for all the changes being made _______to us yet.
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A
has not explained
B
has not been explained
C
did not explained
D
were not explained
推荐题目
By the 1920s, Howard Carter ____ an explorer.
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A
has become
B
had become
C
became
D
would become
I’m glad to see that you ________ a lot of progress since I ________ you last. 
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A
will make; have met
B
have been making; met
C
had made; met
D
have made; meeting
When I jumped into the river, the water ___very cold.
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A
was fell
B
fell
C
felt
D
was feeling