Answer: Efficiency
Step-by-step explanation:
The five sandwich shops constantly competing in an effort to gain competitive advantage over their competitors whilst keeping costs low are adhering to one Porter's competitive advantage theories which is Cost Leadership.
This benefits the industry as a whole because the sandwich companies will keep coming up with new ways and technologies to produce sandwiches at the lowest cost so that can increase their productivity.
Efficiency by definition is to make things at the lowest cost so the sandwich shops constantly aiming to reduce or at least maintain cost while increasing production is going to lead to Industrial Efficiency.