All the options listed can contribute to a school's academic reputation, but among them, the rigor of curriculum (d) is often considered one of the most significant factors. It directly relates to the quality of education and the challenges presented to students.
However, it's important to note that location (a), online reviews (b), and cost of tuition (c) can also play important roles in shaping perceptions of a school's reputation, but they are more contextual factors rather than direct measures of academic quality.