Question

protection of habeas corpus means that
citizens cannot be punished without a trial.
laws cannot apply to past situations.
citizens cannot be held without legal action.
laws cannot include cruel or unusual punishments.

Explanation:

Habeas corpus is a legal writ that protects individuals from unlawful detention. It ensures that a person cannot be held without proper legal process (legal action). The other options are related to different legal principles: "citizens cannot be punished without a trial" is about due process of law for punishment; "laws cannot apply to past situations" is about ex - post - facto laws; "laws cannot include cruel or unusual punishments" is related to the Eighth Amendment (in the US context regarding punishments).

Answer:

citizens cannot be held without legal action.