英语求详细解析Research___all over the world into the possible caus

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英语求详细解析

Research___all over the world into the possible cause of cancer in the past years.
A.was made B. had been made C.has been making D.has been made

可以理解为什么用完成时态,但是,怎么理解这句话?into做为什么的连接介词啊?

大概可以理解为,过去的几年里有做一些关于癌症的可能病因的研究.吧
research into 什么（这里是癌症的起因）

英语求详细解析Research___all over the world into the possible caus 1.Research___all over the world into the possible cause of c 求英语作文travel over the world 英语“Pandas are all over the world 英语people from all over the world all over the world roof over the world All the over the world in the world all over the world in the world around the world 和all over the world的区别,请详细的讲一边 the whole world fell into all over the world造句

英语 求详细解析Research___all over the world into the possible caus