To tell you the truth, it's very hard for us to help them get rid of Internet addiction. But we _________ on this problem trying to improve the situation.
A.worked B.had worked C.are working D.had been working正确答案C
To tell you the truth, it's very hard for us to help them get rid of Internet addiction. But we _________ on this problem trying to improve the situation.
A.worked B.had worked C.are working D.had been working正确答案C
