in a normal frequency distribution of serum sodium concentrations, the mean is 141 mEQ/Land the standard deviation is 3.2mEQ/L which of the following most closely represents the percentage of values in the interval between 137.8 mEQ/L and 144.2mEq/L

a. 25%

b 50%

c.65%

d. 95%

e. 99%