9.
We've discussed this problem
intermittently
, but so far we've failed to come up with a solution.
A、
off and on
B、
time and again
C、
once upon a time
D、
on and after
【正确答案】
A
【答案解析】
intermittently间歇地，off and on断断续续地，time and again反复地，once upon a time从前，on and after自……起，……以后
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