Greek slaves were owned by , while helots were owned by .

Greek slaves were owned by individuals, while helots were owned by the state.                  

Explanation:

Slavery was common among Athenians as they used thousands of slaves to work in their private homes, factories and mines. Slaves captured in war and came from all over the Mediterranean. Slaves were the property of their master. A slave owner could sell, rent, give or leave them. A slave could have a family but not acknowledged by the state, and the master could divide the family members at per his wishes.

Helots were state-owned slaves. There were very much in practice in the ancient Spartans. They were specified to work in a piece of land. They also forced to work in fields as they were serf.

a and c?

i think it is a and c