Regarding PAR (Positive Acknowledgement and Re-transmission), which of the answer choices below are correct?（）

• A、The source device will only retransmit lost packets on the request of the destination device.
• B、The source device starts a timer when it sends a segment and retransmits if an acknowledgment is not received before the timer expires.
• C、The destination device acknowledges receipt of a segment by sending a packet with a new sequence number and the ACK bit sent.
• D、The destination device acknowledges receipt of a segment by sending a packet that indicates the next sequence number it expects.
• E、If the destination device does not receive a segment, all segments are retransmitted.
• F、The source device keeps a record of all segments sent and expects and acknowledgment of each.