Workflow post functions and Automation rule are correct.

Workflow post functions run during a workflow transition and they can update issue fields as part of that transition. If a post function on the transition into the QA status was configured to assign the issue to Priya then every issue that moves into QA will be reassigned automatically.

Automation rule can trigger on events such as a status change and then perform actions like assigning an issue. A rule scoped to the project or to the instance that watches for the QA status and assigns Priya will produce the observed behavior.

Components usually control component leads and can influence assignment at creation when the component lead is chosen. They do not by themselves reassign issues when the status changes to QA unless combined with an automation or workflow step.

Project default assignee is a fallback for newly created issues or for unassigned issues. It does not trigger reassignment on a status transition by itself.

Global automation rule is misleading as listed here. Global automation rules do exist but the general category of Automation rule is the relevant cause and the specific phrasing in this option is not the intended answer.

Workflow validators run checks before a transition to decide if the transition is allowed. Validators do not change issue fields or assign users so they cannot cause the reassignment on their own.

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