Why is it useful for historians to base certain studies on the analysis of geographic regions? a. the particular countries that make up each region do not change over time. b. experience has confirmed that analyzing regions is the most effective approach to history. c. the major historical themes apply only to certain civilizations in certain regions. d. societies located in the same region can affect each other's development.

D. Societies located in the same region can affect each other's  development.

Let's take an example, if you are studying history of the language, it is essential for historians to analize geographic regions since the speaking of a language affects a whole geograhic region regardless of the period. Therefore, when studying history of the Spanish tongue in Latin America, for instance, it is key to study Latin America as a geographic region, since the arrival of inmigrants greatly impacted on the variations of the language which is spoken by different societies in this region nowadays.

the answer is title i subtitle b