Answer:
The correct answer is option B.
Explanation:
There are three very popular supermarkets. Among them, two close at 9 p.m, while Safeway remains open 24 hours a day. Since at midnight Safeway is the only accessible supermarket and there are no close substitutes available, we can say that Safeway has a monopoly at midnight.
Though it does not have a monopoly during the day as there are other supermarkets providing closer substitutes.