Is a Plausible Economic Explanation as to Why Braille―dots‖ Are

is a plausible economic explanation as to why Braille―dots‖ are commonly found on drive-up automatic tellermachines?

A) Blind people must be able use such machines, due to government regulations requiring such dots on the keys under
The Americans with Disabilities Act.
B) The marginal cost of making two different types of keypads is substantial, and the benefit of providing keypads without the
Braille dots is a mere inconvenience to ATM users.
C) The marginal cost of making the keys with the Braille dots is less than making the keys without the Braille dots.
D) There is no economic concept that explains why the keypads have Braille dots.