Refer to the exhibit． What can be determined about routes that are learned from the router at IP address 190．171．23．12?

A、 HQ_Router last received an update from 190．171．23．12 at 3:30 am．
B、 If HQ_Router does not receive an update from 190．171．23．12 in 30 seconds, all routes from that source will be removed from the routing table．
C、 If HQ_Router does not receive an update from 190．171．23．12 in 30 seconds, all routes from that source will be flagged with a hold-down timer．
D、 190．171．23．12 is expected to send an update to HQ_Router for network 190．172．0．0 in 3 minutes and 30 seconds．

【正确答案】 B

【答案解析】