While the salinity levels may vary greatly region to region, there is a consistent difference in density between the various latitudes. Suggest a possible explanation for this observation. SOMEONE PLS HELP THIS IS DUE TONIGHT IN LIKE AN HOUR

Which of the following best describes the purpose of a nation’s boundaries? a. to limit the movement of goods and people b. to make it easier for cartographers to create maps c. to make the movement of goods and people easier d. to prevent other countries from invading territory