Weighted Random Early Detection is a congestion-avoidance mechanism. It starts dropping selected packets before an output queue becomes completely full, which helps avoid tail drop and TCP global synchronization. WRED can weight the drop behavior by IP precedence or DSCP so lower-priority traffic is more likely to be dropped before higher-priority traffic. That makes options A and D correct. WRED does not guarantee delivery of high-priority packets; it only changes drop probabilities. It also does not perform deep flow identification with high granularity, and it is not a protocol-discovery feature. In QoS design, classification and marking identify traffic, congestion management schedules traffic, and congestion avoidance drops early to prevent queue collapse. CCNA 200-301 v1.1 IP Services includes QoS behavior at a conceptual level, and WRED is best remembered as selective early drop based on traffic marking. Reference: Cisco QoS congestion avoidance and WRED behavior.