The expert offered us another piece of advice , of great help to our program.
A. I think it is
B. I think which is
C. which I think it is
D. which I think is
网友回答
A. I think it is
B. I think which is
C. which I think it is
(答案→)D. which I think is
解析：句意为:--专家给我们提出了另一条建议，这条建议我认为对我们的项目很有帮助。
定语从句中缺主语，可以排除A，C。插入语I think，紧跟在特殊疑问词后，且无时态和语态的变化，可排除B. 故D选项正确