What are the three levels of classification under the U.S. system?

The three levels of classification under the U.S. system are indeed Confidential, Secret, and Top Secret. Each of these levels represents a different degree of sensitivity regarding national security information and dictates how that information is handled, shared, and stored.

Confidential is the lowest classification level and is assigned to information that could cause damage to national security if disclosed. Secret information is more sensitive and could cause serious damage if revealed. Top Secret is the highest classification and is used for information that could cause exceptionally grave damage to national security if disclosed.

The other choices represent various terms that do not align with the standard classification levels established by U.S. government policy. For example, terms like Major, Moderate, and Minor do not exist within the formal classification framework, and neither do Restricted, Classified, and Unclassified fit the classification levels, as "Classified" itself is a blanket term that encompasses Confidential, Secret, and Top Secret but is not a classification level on its own. Additionally, High, Medium, and Low are not recognized classification levels within the U.S. system. Hence, the correct answer reflects the established and recognized framework for classifying sensitive information in the context of national security.