Question

The PRIMARY obstacle to population growth in the area known as the "Canadian Shield" is that

Answer 1

The exposed portion of the continental crust underlying North America refers to Canadian Shield. The continental crust is known as the North American Craton which consists of rocks from the Archean dn Proterozoic eons and extends from Mexico to Greenland. Canadian Shield also produces great resources that helped most humans for their economic development. Because of the resources present in the Shield, it has a great disadvantage to settlers. The primary obstacle to population growth in the area is the presence of the bare rock, thin soils, muskeg and insects. So the answer is letter A.

Answer 2

Hint: it relates to something humans must have to survive.

The area known as the "Canadian shield" is not capable of intensive agriculture output. The area lies in the northeastern portion of the country and consists of a thin layer of soil over a foundation of bedrock. This yields very little in the way of agricultural output.

so your answer will be the area is  not capable of intensive agriculture output.