Packet-switching　wireless　networks　are　preferable(66)when　transmissions　are(67)because　of　the　way　charges　are(68)per　packet.　Circuit-switched　networks　are　preferable　for　transferring　large　files　or　for　other　lengthy　transmissions　because　customers　are(69)for　the(70)of　time　they　use　the　network.