Could you explain to me the answers and what is meant by closing entries ?

Summerhill Corporation had the following trial balances at its year-end (before closing entries). All accounts had normal debit or credit balances 4. Cash Equipment Revenue Supplies expense Unearned revenue Salaries expense $250 150 400 200 70 60 One of the required closing entries should have Retained Earnings a) Credited for $400 b) Debited for $200 c) Debited for $400 d) Credited for $260