You are deploying two core switches， one in each building， 50 km away from each other. The cross-connection between them will be a Layer 2 2-gigabit EtherChannel with an 802.1Q trunk. You configured it correctly but the link does not come up. The port is in the "admin up" state， and the line protocol is in the "down" state. The fiber link is OK. What would be the most likely reason for the link not to come up？（）

• A、The switches are not the same model.
• B、You are not using the correct SFP.
• C、You are not using correct optical media converters.
• D、Configuration should be modified， because the distance is longer.