答案：B

题目分析：考查非谓语动词，分词做状语，介词后跟动名词，所以选B，句子意思“他学习很刻苦，目的是通过考试”

点评：由句子可以知道，它不是谓语动词，只是作状语。做非谓语动词时，首先分析句子成份，看句中是否有谓语

即学即练：You should understand the traffic rule by now． You’ve had it_______ often enough．

　A． explaining B． to explain C． explain D． explained

解析：D