Apart from flooding and diarrhea, World Health Organization also observed ______.

A．He and his co-workers followed 997 healthy Catholic nuns, priests and Christian brothers within 12 years.
B．He hasn’t yet found out the underlying reasons why conscientiousness has an impact on Alzheimer’s risk.
C．He suggests that people with more active frontal brain regions are more careful and conscientious.
D．He thinks that increased activity in frontal brain regions may compensate for a decline in function in other brain regions.