sory for typo, its A,D, E

The correct ans is A,B and E because when a user hit save button, all Validation Rules will fired, if nothing fit into custom validation rules defined, workflow will kick-in and if there is any field update, validation rules will not fired again. more over, Salesforce processes any rules in the following order:
Validation rules
Assignment rules
Auto-response rules
Workflow rules (with immediate actions)
Escalation rules

The right Answer is A D E. Workflow rules and some processes can invalidate previously valid fields. Invalidation occurs because updates to records based on workflow rules and also on process scheduled actions don’t trigger validation rules.