A offers to B to sell him a parcel of land for $5,000, stating that the offer will remain open for thirty days. B replies, I will pay $4,800 for the parcel, and on A's declining that, B writes, within the thirty day period, I accept your offer to sell for $5,000. I accept your offer to sell for $5,000, is:

1. An acceptance.
2. A new offer.
3. A counteroffer.
4. A rejection.