Answer B,E is correct: B. Topology changes are occurring within spanning-tree; E. The forwarding table has overflowed. A switch floods frames when it does not have a usable destination MAC entry. Spanning-tree topology changes can flush or age MAC table entries, forcing unknown-unicast flooding until the switch relearns addresses. A forwarding table overflow, including a CAM table overflow attack, also causes flooding because the switch cannot maintain complete MAC-to-port mappings. A defective patch cable usually causes physical errors, CRCs, or link instability, not ordinary frame flooding. Globally configured port security is not itself a flooding trigger. Cisco CCNA 200-301 v1.1 Network Access tests this because excessive flooding can look like a performance problem while the root cause is Layer 2 learning instability. The corrected choices are topology changes and forwarding-table overflow.