It was not until the beginning of the twentieth century________to explore space.
#93086
A
did man begin
B
when man began
C
that man began
D
then man began
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This problem is said _____ three times. 
#92660
A
having discussed
B
to have been discussed
C
having been discussed
D
to have discussed
______put great pressure on the local government to tell the truthfulness of the tiger photo as soon as possible.
#93252
A
The great loss of lives in the mine
B
The human cases of bird flu
C
The customers’ complaints
D
The questions from people especially experts