Answer:
C) Increase in the demand for muffins.
Explanation:
Substitute goods are alternative goods because they can be replaced by each other.
For example: Coco cola and Pepsi are substitute goods, if coco cola is not available people can choose Pepsi without any problem.
So, If the price of bagels increases, it will directly leads to the increase in demand of muffins. Because when people can choose muffins at cheapest rates, why would they go for bagels? When both are substitute goods.