Explanation

The actual average distance of Neptune from the Sun is closer to 30 AU but not exactly 30 AU based on precise modern data. Option A (28) is incorrect as it is a specific number that does not match the accepted value. Option C (32) is incorrect as it is too far from the established average distance. Option D (None of these) is likely correct because the actual value is often cited around 30 AU, but given the options and potential for slight variations or outdated data, 'None of these' is the safest choice if 30 AU is not considered precise enough.