Answer:
Patrick is eating a cake.
Step-by-step explanation:
A simple subject is the "who" or "what" that does the verb. 
A compound verb is a combination of two verbs that combine to make a compound verb. It is formed by the combination of a helping verb with another verb. 
A direct object is the receiver of the action of the subject. 
In the sentence "Patrick is eating a cake", Patrick is the simple subject. "is eating" is the compound verb as "is" is a helping verb fused with another verb "eating". And lastly, "cake" is the direct object. 
Thus, a sentence with a simple subject, a compound verb, and a simple direct object is "Patrick is eating a cake."