<span>Severe depression that has a sudden onset or seems not to have any
external cause whatsoever is called major depression. Major
depression is sometimes referred to as </span>unipolar disorder or major
depressive<span> disorder (MDD); typical signs of MDD include
persistent feeling of sadness or a lack of interest in outside stimuli.</span>
Family history is the top risk factor for a person to get an Alzheimer's disease. This is because of heredity that a person cannot escape from. So it is important that a person must know the family history whether he or she can be a dominant carrier of this disease or not.
D. Smallpox is your answer
