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93. The diligent student refused the help of others and insisted on working out the difficult maths problem _____.

93. The diligent student refused the help of others and insisted on working out the difficult maths problem _____.

A. on his own               B. in his own                C. of his own                D. for his own

93. The diligent student refused the help of others and insisted on working out the difficult maths problem _____.