A network engineer notices an unusual pattern of interface errors on a router connecting the company's data center to the Internet. The errors include a high number of runt frames and CRC errors, primarily occuring during peak hours.

What could he the MOST likely cause of these errors?

a $)$ The DNS server is not responding

b$)$ The firewall is blocking incoming traffic

c$)$ The router is configured with an incorrect IP address

d$)$ There is a duplex mismatch between the router and the upstream device.