Final answer:
Walmart stores were the largest corporation based on revenue according to the Fortune Global 500 companies for 2012, maintaining its top position into the 2020 ranking as well.
Step-by-step explanation:
The student asked which corporation was the largest based on revenue according to the Fortune Global 500 companies for 2012. Among the options provided, Walmart stores were indeed the largest corporation based on revenue in 2012. This can be validated by the information provided that indicates Walmart topped the list of the Fortune Magazine Global 500 in 2020 as well, followed by Sinopec Group, State Grid, China National Petroleum, and Royal Dutch Shell. It's noteworthy that when companies like Walmart are compared in terms of economic size, they can be larger than the economies of many nation-states.