Answer:
D. human geography
Step-by-step explanation:
"Human geography" is the study of the world, including the people living on it, the communities they form and the different cultures they share across different parts of the world. It shows how people relate to the different places they're living in. This includes human settlement or migration and human distribution.
In the question above, the geographer wants to learn about people's movement around the world. This is clearly a part of the study of human geography because it is related to how the people are distributed around the world in relation to their reasons for choosing specific locations.
This explains the answer.