Explanation:

- Collective Economic Paradox:

- This term suggests a situation where what's true for the collective economy might not hold true for individual components. This is a definitive limitation of macroeconomics as it generalizes the economy.

- Ignores Individual Units:

- Macroeconomics focuses on the economy as a whole and often neglects the detailed study of individual units such as households and firms. This can overlook critical insights from micro-level interactions.

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

- Macro Economics faces both of the above limitations, as it cannot delve into detailed individual behaviors and sometimes generalizes too broad, causing paradoxes.

- Option 4 - None of these:

- This isn't correct as both (a) and (b) are valid limitations of macroeconomics.