Marketing department users report network performance degradation in the morning and early afternoon, but sales...

From the configuration, the Sales and Customer Service ports are hard-set to full duplex, 1000 Mbps, while the Marketing interface (GigabitEthernet0/3) is set to duplex auto and speed auto. CompTIA A+ explains that mismatched or lower-negotiated speeds and duplex settings can cause noticeable network slowdowns, collisions, and retransmissions—especially at busy times of the day when utilization is high.

Because all cabling is Cat 5e, it fully supports Gigabit Ethernet, so the cabling is not the limiting factor. The IP addresses are all in the same subnet (192.168.1.0/24) and formatted correctly, so there is no subnet or addressing problem. That rules out options A and C.

With speed auto, the Marketing port may be negotiating only 10/100 Mbps, or even a duplex mismatch (e.g., half duplex vs full). This would severely limit throughput compared to the gigabit links used by the other departments. In peak periods, that slower link would become congested first, which matches the users’ reports of performance degradation only in Marketing.

Therefore, the most likely cause is that the Marketing interface is operating at 10/100 instead of 1000 Mbps, making option D correct.