A University customer has a BladeCenter H fully populated with LS21 Blades， a single AMM， and four power modules. The BladeCenter has been running flawlessly for three months. One day an administrator discovers that they cannot view video on blades 9-12 either locally or remotely even though they still appear to be running. The video works on all of the other blades. Which of the following is the cause of the video problem？（）

• A、A power module has failed and there is not enough power to see video on all blades.
• B、MUX 3 on theBladeCenter backplane has failed.
• C、A firmware update is required on the AMM.
• D、A second AMM is required to view video on blades 9-14.