What Is the Medical Definition of Dementia,and What Is One

What is the medical definition of dementia,and what is one example of dementia?

A) Dementia is a violent condition where an individual poses a criminal threat to him- or herself and others.An example is pyromania.
B) Dementia is an impairment of mental function characterized by memory loss,confusion,and disorientation.An example is Alzheimer disease.
C) Dementia is an irrational,obsessive fear.An example is agoraphobia.
D) Dementia is a loss of consciousness.An example is coma.