We usually are so hungry at lunch, we eat whatever the cafeteria staff has decided to cook.

what is the function of the underlined noun clause?

a. subject
b. indirect object
c. direct object
d. predicate nominative

The underlined noun clause in this sentence is "whatever the cafeteria staff has decided to cook". And this underlined noun clause functions as a direct object. The correct answer would be option C. This noun clause directly receives the action of the verb "eat". 

The answer would be logical.