A series of attempts________made, he came to a successful solution of the problem.

【正确答案】 D

【答案解析】解析：“make attempts to”即“尝试着做某事”。根据后半句的时态可知前半句的时态应当是现在完成时，其中A series of attempts充当逻辑主语，需采用被动语态。所以正确答案为D。