Final answer:
Polynices brought six great heroes with him when he attacked Thebes, hence the correct answer is (a) six.
Step-by-step explanation:
The question regarding how many great heroes Polynices brought with him when he attacked his brother is from the Greek tragedy written by Sophocles, which refers to the story of the attack on Thebes. Polynices brought with him six other heroes, making a total of seven including himself.
This group is known as the "Seven Against Thebes" and is a well-known part of Greek mythology and literature, highlighting ancient Greek culture and storytelling.