The correct answer is A. 1 person per sq. km.
A hunting and gathering economy is a type of economy in which people obtain food by hunting animals and gathering wild plants. This type of economy is very labor-intensive, and it requires a lot of land to support a small number of people. In general, a hunting and gathering economy can support only about 1 person per square kilometer.
Option B is incorrect because it is too high. A hunting and gathering economy cannot support 3 people per square kilometer because there is not enough food available to support that many people.
Option C is incorrect because it is too high. A hunting and gathering economy cannot support 5 people per square kilometer because there is not enough food available to support that many people.
Option D is incorrect because it is too high. A hunting and gathering economy cannot support 7 people per square kilometer because there is not enough food available to support that many people.