There is still quite a long way to go ________ researchers can

There is still quite a long way to go ________ researchers can find a solution to the problem.
A、before
B、until
C、so
D、where
【正确答案】：A
【题目解析】：There is still a long way to go before+分句是固定句型表示要…还有很长的路要走，离…还很遥远。此句话的意思是研究人员离找到问题的解决方法还很远。