Answer:
b.the value of the knowledge she would have received had she attended class.
Step-by-step explanation:
Opportunity cost is defined as the loss of benefits or profit that could have been gotten by choosing a particular thing over the other. For example, choosing to buy processed food over cooking.
The opportunity cost there is the loss of cooking skill that would have been gotten had the person prefered to cook over buying processed food.
In the case of Ellie, her opportunity cost is the value of knoeledge she could have gotten had she decided to sacrifice her sleep ( the 2 hours nap she took ).