Complete subject is a subject and modifiers describing the subject.
Example:
My friend, George, is very good at math.
"My friend, George" would be a complete subject.
Compound subjects contain multiple (two or more) subjects that share a verb and are joined by a conjunction.
Example:
Apples, Bananas, and Oranges are all fruits.
"Apples, Bananas, and Oranges" would be a compound subject.
A simple subject is one subject with no modifiers and no conjunctions.
Example:
I got new headphones today.
"headphones" would be a simple subject.
"Galileo, Copernicus, and Kepler" are multiple subjects that share a verb phrase and are joined by a conjunction.
So the answer is B. compound subject.
