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                题目内容
                (国家开放大学英语语法)
            
            
                He studied hard at school when he was young, _____ contributed a lot to his success.
A.which
B.therefore
C.that
D.what
                    
                    
                    
                
                
                
            
        A.which
B.therefore
C.that
D.what
参考答案