[填空题]Which subject is the book about

[填空题]Which subject is the book about

[单项选择] A subject which seems to have been insufficiently studied by doctors and psychologists is the influence of geography and climate on the psychological and physical health of mankind. Them seems no doubt that the general character of the landscape, the relative length of day and night, and the climate must all play a big part in determining what kind of people we are. It is true that a few studies have been made. Where all the inhabitants of a particular area enjoy exceptionally good or bad health, scientists have identified contributory factors such as the presence or absence of substances like iodine, fluoride and calcium (氟化钙), or iron in the water supply, or perhaps types of land that provide breeding places for pests like mosquitoes or rats. Moreover, we can all generalize about types of people we have met. Those living in countries with long dark winters are apt to be leas talkative and less spirited than inhabitants of countries where the climate is more moderate. And w
A. focus on some unknown aspects
B. be pursued on a larger scale
C. go much deeper
D. be carried out within a larger scope