Arthur,a 70-Year-Old,and Kevin,a 24-Year-Old,are Given the Same Dose of a Certain

Arthur,a 70-year-old,and Kevin,a 24-year-old,are given the same dose of a certain water-soluble drug X.When Dr.Robinson examines samples of their blood plasma,he finds that the concentration of X in Arthur's system is much higher than the concentration of X in Kevin's system.Why is Arthur's blood plasma more concentrated with drug X than Kevin's blood plasma?

A) Because elderly people have a lower percentage of total body water than younger people do
B) Because elderly people have more lean body mass than younger people do
C) Because elderly people have less adipose tissue than younger people do
D) Because elderly people have less intestinal absorptive surface area than younger people do