阅读短文,选择正确的答案（英语）
Henry is very fat.He can't walk fast for a long time and he often feels tired.He wants thin,so he eats very little.He eats a little suger,because it will make himfat.He does some esercise every morning.He often goes to swim and runs in the afternoon.Now he is thinner than before.
Henry's cousin,Susan,is healthier( )him.She takes care of herself.She does a lot of exercise every week,and keeps is good health.
（ ）中应该填入什么?
A;as B:of C:to D:than
请说明理由，