He gave us another piece of advice, of great help to the research work.
A. which I think is
B. which I think it is
C. I think which is
D. I think it is
网友回答
(答案→)A. which I think is
B. which I think it is
C. I think which is
D. I think it is
解析：考查从句，首先分析句子，从句of great help to the research work.缺少主语和谓语，又是个非限制性定语从句，所以选A