Explanation:

- Option 1: Domestic price levels in different countries vary due to differences in economic conditions, inflation, and market factors. Comparing these can illustrate cost of living or purchasing power disparities.

- Option 2: GDP comparisons need standardization because a nominal GDP figure in one country might not reflect equivalent economic size or wealth in another due to currency value differences.

- Option 3: Both statements hold value for making meaningful cross-country economic comparisons, looking at both domestic price levels and GDP values.

- Option 4: None is incorrect as utilizing common price levels aids in comparisons.

Option 3: Both is correct for comparing economic metrics across nations.