Focusing on a narrow range of products/services that can be produced most efficiently and cost-effectively
A
Tariffs
B
Human Capital
С
D
Enterprise
Specialization

Specialization

Explanation:

Focusing on a narrow range of products or services that can be produced most efficiently and cost-effectively is referred to as specialization.

Specialization simply refers to a method whereby an economic agent focuses on the goods that it can only produce efficiently and also minimize cost for. This helps in the production of more goods and also improvement in revenue.

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).

(d) take jobs from american workers.