When a user tries to log into the system, the following error occurs:  "3004-004. You must "exec" login from the lowest login Shell". Which of the following procedures should be performed next to determine the cause of the problem?（）

• A、 Reboot the system. 
• B、 Increase the number of ptys. 
• C、 Increase number of licenses. 
• D、 Run df -k to check for full filesystems.