考查词组辨析。A选项on occasion“间或,有时”,例句:It has,on occasion,created trouble for the bank. (有时,这给银行造成麻烦。);B选项on purpose“故意”,例句:I came here on purpose to see you.(我特地来这里看你。);C选项on condition“在……条件下,如果,倘若”,例句:You can go out on condition that you wear an overcoat. (你要穿上外套才能出去。);D选项only if“只要,只有”。用于句首时,后面主句的主谓语要倒装,例如:Only if a teacher has given permission is a student allowed to enter this room.(只有得到老师的允许,学生才可以进这屋。)。四个选项中只有C选项on condition后面跟that从句,表示“在……条件下”。句意:他向我借钱,我同意了,但条件是下周还钱。综上所述,本题的正确答案是C选项。