Under what circumstance may an aircraft deviate from an active Air Traffic Control clearance without obtaining an amended clearance?

1. Only in an emergency requiring immediate action, or in response to an ACAS/TCAS Resolution Advisory (RA).
2. Whenever the pilot-in-command determines that a shortcut is safe and will save fuel.
3. When operating under Visual Flight Rules (VFR) in visual meteorological conditions (VMC).
4. During normal daylight operations when no other traffic is visible to the pilot.