Consider a production possibilities curve for an economy producing food and clothing. Under what circumstances is it possible to increase the production of food without sacrificing clothing?

1. when the production possibilities curve shifts outward due to decreased immigration (which reduces the labour force)
2. when the economy moves from one point on the production possibilities curve to another point on the curve
3. when the economy moves from a point outside the production possibilities curve to a point inside the curve
4. when the production possibilities curve shifts outward due to technological progress