The study of agriculture is fundamental to the discipline of human geography because:
a. human geography studies the human relationship with the physical environment, and the ways that people interact with and transform their physical environments to meet their food needs is a fundamental aspect of that relationship
b. the study of agriculture makes clear how difficult it is to maintain a clear distinction between "people" and "Nature," or between human activity and natural processes
c. it is impossible to understand other topics and themes of interest to human geographers, including globalization, urbanization, and migration, without paying careful attention to social systems of food production and distribution
d. all of the above