Refer to the exhibit.

The reason the administrator cannot access the EC2 instance could be:

D. The directory location of the .pem file is incorrect.

SSH Key Location: When initiating an SSH connection to an AWS EC2 instance, you must specify the private key file (.pem file) location that corresponds to the public key used when the instance was launched. The error "Warning: Identity file Staging-key.pem not accessible: No such file or directory" indicates that the SSH client cannot find the .pem file at the specified location.

Correct File Path: The administrator needs to ensure that the path to the Staging-key.pem file is correctly specified when running the SSH command. If the file is not in the current directory from which the command is executed, the full or relative path to the file must be provided.

References: This behavior is in line with standard SSH connection practices and AWS guidelines for accessing EC2 instances. It is a common issue that occurs when the private key file is not located in the directory from which the SSH command is being executed or the path provided is incorrect.