—Was ________ problem solved?

—We were trying to think of ________ way out, but it was difficult to find one.

A．a; a

B．a; the

C．the; a

D．the; the

除（）外，其它三个方面都显著影响调查结果

A、调查工具前后一致与否

B、操作员素质水平高低

C、使用诱饵前后一致与否

D、蟑螂密度适中与否