The twins are so much-------and it is difficult to tell one

The twins are so much_______and it is difficult to tell one from another.
为什么用alike,而不可以用similar或者like.
好像这两个词也都可以做表语啊
similar的解释可以接受
LIKE可以做表语,我查了下
The twin brothers are very much alike．这对双胞胎兄弟非常相像.
The twin brother is like that one very much．（介词作表语）这对双胞胎兄弟中一个很像另一个.