What Was the "American Plan" Concept of Employment

What was the "American plan" concept of employment?

A) It guaranteed equal pay for men and women.
B) It established closed shops where the employer could only hire union workers.
C) It established open shops where the employer could hire anyone.
D) It guaranteed workers an eight-hour workday and weekends off.
E) It honored the progressive promise of a cleaner, safer working environment.