Fix versions is the correct choice.

When a subtask is created under an existing parent issue, Jira generates the subtask in the same project and carries over several contextual fields from the parent. Fix versions are not copied to the subtask by default because version assignments represent planned releases at the parent issue level and are typically managed separately for subtasks.

Sprint assignment is incorrect because the sprint field is inherited by the subtask when it is created on the same board or sprint, so the subtask will have the same sprint as the parent.

Issue security level is incorrect because the subtask inherits the parent issue's security level at creation according to the project security scheme unless it is changed afterwards.

Project is incorrect because a subtask must exist in the same project as its parent and it therefore inherits the project automatically when created.

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