hadbeenstudied和hadstudied有什么区别?还有请回答下面的问题^o^Mr.WuinAmericafortwoyears.NowonderhecantalkwitnforeignersnowattheofficeinChina.为什么答案是“studied”而不是“hadstudied”

Question

had been studied和had studied有什么区别?还有请回答下面的问题^o^
Mr.Wu_______in America for two years.No wonder he can talk witn foreigners now at the office in China.为什么答案是“studied”而不是“had studied”

Answer 1

had been studied是被动语态,被研究.had studied是研究,表示主动.
至于下面的句子,后面说他现在可以和外国人交流,前面要用一般过去时,表示他曾经在美国学习了两年.不需要用过去完成时.