This is a reason the keyboard design wouldn’t change, even when the technological limits are no longer present. People grew up with the slower-typing design and still want it today. This is why the fact people still use the design today doesn’t undermine Cora’s explanation.

Bernard believes the fact people still use the same design shows that the design couldn’t have been intended to slow people down. (B) simply affirms that the same design is used today, which we already knew. But it doesn’t suggest why the same design is used today, unlike (A).

Pointing out that the design still allows fast typing doesn’t engage with Bernard’s reasoning. We want to show how the design could have been intended to slow people down, despite the fact we still use the design today.

This supports Bernard’s reasoning. After all, why aren’t people changing to a faster layout if we don’t need to slow people down anymore? Bernard’s suggestion is that the lack of change implies slowing people down couldn’t be the original purpose of the design.

This supports Bernard’s reasoning. If the keyboard can be changed to accommodate a different layout, then why hasn’t the keyboard changed if it was originally intended to slow people down? To Bernard, the lack of change implies the original purpose wasn’t to slow down typing.