The nominal distance of a boundary layer is defined as the distance from the wall to a point (a) where the velocity is 99% less than the asymptotic limit (b) where the velocity ceases to be laminar...

The nominal distance of a boundary layer is defined as the distance from the wall to a point

(a) where the velocity is 99% less than the asymptotic limit

(b) where the velocity ceases to be laminar

(c) where the velocity is within 90% of the asymptotic limit

 (d) where the velocity is 99% of its asymptotic limit