Answer:
a. either immigration from abroad increases or technology improves.
Explanation:
A long-run aggregate supply curve is a concept in economy that mentions to the output that an economy can produce when utilizing all its parts or elements of production.
When a long-run aggregate supply curve shifts right means that the production increases and economy rises. And that is true only when technology increases or immigration increases.
Thus the answer is --
a. either immigration from abroad increases or technology improves.
