---

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.
（4.0分）
4.0 分

A、

had worked
B、

are working
C、

had been working
D、

worked

---

出自：郑州航空工业管理学院-大学英语

显示答案