In an open-loop payment network, the end parties ____, while in a closed-loop payment network, they ---- enter into agreements with the network; enter into agreements with banks belonging to the network enter into agreements with banks belonging to the network; enter into agreements with the network are not charged a fee each time they use the network; are charged a fee each time they use the network can withdraw from the network at any time; have to sign a long-term contract with the network