單項(xiàng)選擇題

以下哪個(gè)信令可以發(fā)起GPRS上行資源請(qǐng)求:()

A.Packet Downlink Ack/Nack
B.Packet Downlink Assignment
C.Packet Downlink Dummy Control
D.Packet Uplink Ack/Nack

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