I think the answer is B. Geographers use different kinds of maps, depending on the subject they are studying. <span />
The name for such a hole is "caldera" which is a word of Spanish origin meaning "a pot" or a "cooking pot" (thing of cauldron!) - and this word is used because it resembles the shape of this hole.
Often the Calderas are filled with water forming lakes and often there is an island in the middle of the water.
GIS is basically used to study geologic features and etc, it creates 3D displays of geographic features
I know jobs for one, over population maybe, and because they are worried that dangerous people could be entering into the country with intention to harm. (unless this is a "only 3 right answer" kind of thing)
Canadian shield is composed of Precambrian rocks that cover 2.8 million square miles.
