of the two pens, which is the better?

为什么要加the?
better前为何加the，不用可以吗？why？？？

of the two pens, which is the better? Of the two pens,which is_____? _____为什么填the better...Neither There are a pencil and two pens on the desk. the two of them I have two pens,one is red,____ two are black. the other Leaders of the two neighboring...... The two of English prastices .I have bought two ball pens , ____writes well. 为什么 填neither of wich? two of us和the two of us 的区别 B is the shortest of the two.