单选题：根据以下内容回答题:Happiness can be described as a positive mood and

根据以下内容回答题:
Happiness can be described as a positive mood and a pleasant state of mind．
According to recent polls sixty to seventy percent of Americans consider themselves to be moderately happy and one in twenty persons feels very unhappy．Psychologists have been study-ing the factors that contribute to happiness．It is not predictable nor is a person in an apparently ideal situation necessarily happy．The ideal situation may have little to do with his actual feel-ings．
A good education and income are usually considered necessary for happiness．Though both may contribute，they are only chief factors if the person is seriously under-educated or actually suffering from lack of physical needs．
The rich are not likely to be happier than the middle-income group or even those with very low incomes．People with college educations are somewhat happier than those who did not gra-duate from high school，and it is believed that this is mainly because they have more opportuni-ty to control their lives．Yet people with a high income and a college education may be less happy than those with the same income and no college education．
Poor health does not rule out happiness except for the severely debilitated or those in pain．Learning to cope with a health problem can contribute to happiness．Those with a good sex lifeare happier in general，but those who have a loving affectionate relationship are happier than those who rely on sex alone．Love has a higher correlation with happiness than any other factor．
It should be noted that people quickly get used to what they have，and they are happiest when they feel they are increasing their level no matter where it stands at a given time．
Children whose parents were happily married have happier childhoods but are not nece—ssarily happier adults．
The best formula for happiness is to be able to develop the ability to tolerate frustration，to have a personal involvement and commitment，and to develop self-confidence and self-esteem．
According to the article，happiness is greatly dependent upon__________ ． A．happy childhood
B．great wealth
C．a feeling that conditions are improving over what they were
D．a college degree