在货币的流通速度一定且其他条件不变的情况下，商品价格总额增加一倍，流通中所需要的货币量( )。

A．必定会增加一倍

B．必定会增加两倍

C．必定会减少一倍

D．必定会减少两倍

A long-term health study that followed a group of people who were age 35 in 1950 found that those whose weight increased by approximately half a kilogram or one pound per year after the age of 35 tended, on the whole, to live longer than those who maintained the weight they had at age 35. This finding seems at variance with other studies that have associated weight gain with a host of health problems that tend to lower life expectancy.
Which one of the following, if true, most helps to resolve the apparently conflicting findings ？（）

A．As people age, muscle and bone tissue tends to make up a smaller and smaller proportion of total body weight.

B．Individuals who reduce their cholesterol levels by losing weight can thereby also reduce their risk of dying from heart attacks or strokes.

C．Smokers, who tend to be leaner than nonsmokers, tend to have shorter life spans than nonsmokers.

D．The normal deterioration of the human immune system with age can be slowed down by a reduction in the number of calories consumed.

E．Diets that tend to lead to weight gain often contain not only excess fat but also unhealthful concentrations of sugar and sodium.