Explanation:

- Option 1: State of full employment in the economy

- Classical theory often assumes that markets clear, leading to full employment.

- It posits that unemployment is mostly voluntary or frictional.

- Option 2: No possibility of over-or under-production in the economy

- The classical model suggests that supply creates its own demand ('Say’s Law').

- This implies a balance between production and consumption, avoiding over-production or under-production.

- Option 3: Both (a) and (b)

- Both full employment and balanced production as per classical theory are combined here.

- Option 4: None of the above

- This option would imply disagreement with both classical claims.

The correct answer is Option 3: Both (a) and (b). The Classical Theory does align with both those statements.