Fiber connections require Tx on one end to connect to Rx on the other end. If the patch cord is replaced and link lights remain off, the most common cause is that the connectors are reversed. Swapping (transposing) the connectors ensures proper transmit/receive alignment.

A. Replacing the transceiver may eventually be necessary, but only after verifying correct connections.

B. Restarting the switchport won’t resolve a physical misconnection.

D. Using multimode fiber would be incorrect here, as the link was designed for single-mode (10 miles/16 km requires SMF).

References (CompTIA Network+ N10-009):

Domain: Network Troubleshooting — Fiber connectivity, Tx/Rx alignment, link light diagnostics.