Bela Balassa's explanation for why haircuts are cheaper in Mexico than in Norway also explains why personal servants are cheaper in Mexico than in Norway because: a. the hourly wages of barbers and personal servants are equal in Mexico and equal in Norway b. the explanation is based on average productivity in the entire economy, not just among barbers c. the productivity disadvantage that Mexican barbers face is about equal to the productivity disadvantage that Mexican personal servants face. d. the explanation is based on inflation rates for the whole economy