Answer:
This mistake is clearly a result of human and design error
Step-by-step explanation:
Design errors are those errors that cause human beings to make mistakes.
This question says that the computer did not state the keys that were available for each room. This must have given off the impression that all rooms were occupied to Susan.
On her own part, her failure to note the rooms that she gave out their keys is part of why this mistake happened. This is human error from her part.