Final answer:
The closest antonym for 'curtail' is 'expand,' which means to increase in size or quantity, in contrast to 'curtail,' which means to reduce or cut short. The correct answer is option A.
Step-by-step explanation:
The closest antonym for the word 'curtail,' as it is used here, would be 'A. expand.' To curtail something means to reduce in extent or quantity; to impose a restriction on an activity or cut it short. Therefore, the antonym must be a word that conveys the opposite meaning, which is to increase or make larger. 'Expand' fits this definition, whereas 'diminish' and 'hinder' are synonyms for curtail, and 'transform' does not pertain to the concept of size or scope.