Children usually do not become aware of their ethnic identity until after the age of 12

According to the article Over the Hill about the Betula study of adult cognition, long term longitudinal studies:

(a) are the best way to study aging (b) are very common (c) end up with unrepresentative samples (d) are no longer being conducted

The most common type of genetically inherited intellectual developmental disorder is ______

a. Klinefelter's syndrome c. fragile X syndrome b. Turner's syndrome d. Korsakoff's syndrome