Which Is Not True About the Incidence of Stuttering in Various

Which is not true about the incidence of stuttering in various groups?

A) it may be somewhat lower in cultures reported to have little concern about speaking abilities
B) it is higher than the average among some groups of mentally disabled persons
C) it is lower than the average in the hearing-impaired population
D) It is very low in the lowest social-economic strata (layer) .