What factors could lead to a gap between the average costs of established firms and potential entrants?( )
选项：

A:Firms already in the industry may control a crucial input.
B:Firms already in the industry may be able to borrow investment funds at lower interest rates.
C:Firms already in the industry may have access to superior production technologies.
D:Firms already in the industry may have built plants in the most desirable locations.