— Did you find the missing couple in the mountain yesterday?

— No, but we ____ to get in touch with them ever since. [ ]

A. have tried

B. have been trying

C. had tried

D. had been trying

同一只股票，其风险是客观的，但是有的人买有的人卖，这可能是因为买者和卖者的风险认知度有差异。( )