单选题Careful study shows that&

问题补充：

单选题Carefulstudyshowsthatthebestathleteswin____,_____theythinkthencanwin.A.mostly, becauseB.almost; asC.partly; forD.nearly; since

答案：

A解析考查副词词义辨析和连词的词义辨析。依据句意前果后因，前面的空应是大多数为佳。