Activity A lasts 4 days. B lasts 6 days after A. C lasts 3 days after A. D lasts 5 days after B and C. With unlimited resources, which action shortens the project by two days?

1. Reduce B from 6 days to 4 days without changing other dependencies
2. Start C one day earlier while leaving B and D unchanged
3. Reduce C from 3 days to 1 day
4. Increase parallel reporting on both B and C without changing durations