这里的that= the one. that表示特指,既可以代替单数的可数名词,也可以替代不可数名词; 其复数为those. 而one只能代替可数名词：
This tea is better than that (=that tea).
This book is dearer than that (= the one) on the desk.
These books are dearer that those (= the ones) on the desk.