What action did Charlie take that exemplifies involuntary servitude when dealing with Betty?

Involuntary servitude is a condition in which an individual is coerced into providing labor or services against their will, often through the use of threats or intimidation. In this scenario, the action taken by Charlie that exemplifies involuntary servitude is the use of threats to ensure Betty's compliance. This demonstrates a clear power imbalance and coercion, as it relies on fear to control her actions and restrict her freedom.

The other options illustrate more supportive or voluntary interactions. Offering a safe place to live or allowing someone to leave freely suggests consent and aid, while helping someone learn self-defense implies empowerment rather than coercion. These actions do not reflect the characteristics of involuntary servitude, which fundamentally involve manipulation and control through fear. Therefore, the act of threatening Betty clearly aligns with the definition and practice of involuntary servitude, as it directly forces compliance through intimidation.