💡 Detailed Explanation
The sentence is about making up for a 'shortfall' (不足分) in tuition. '補う' (oginau) means to supplement or compensate for something that is lacking, and it is the most appropriate word for covering a financial deficit. '埋める' (umeru) means to fill (a hole) and can be used figuratively, but '補う' is more natural for a shortfall. '補足する' (hosoku suru) means to add supplementary information. '補充する' (hojū suru) means to replenish or refill something that has been used up.