3 Combobox linked and have relationship

Hi

I have some problem with my project and I was searching through the internet to find the answer but I got nothing!

So, my scenario is:
I have 3 lists and I want to create 3 comboboxes.
Comboxbox 2 is dependent to combobox 1 and combobox 3 is dependent to combobox2. However I want the values to be shown only once.
But I have some duplicate data and I don't know how to show them once in combobox1?
also, I dont know how to linked 3 comboboxes?

I hope you can help me!

I can fixed the duplicate data in comboBox, but still no result in making relation!

You need that in vba or just excel formula? I can do that by validation

If it works, I appreciate your help

What are the values in box 1? box2 and box 3?

What's the relationship you want to add? Only let me write in box2 if box1 is not blank?

I can only do that by validation in excel cell. Not in VBA code, so i wont be the best help..

Thank you
I find the answer

First I create UserForm with 3 ComboBoxes. Then I add this code to UserForm and it works!

HTML Code: 

I used this code to create comboBox1 but i dont know how to make a relation between comboBox1 and 2 and 3 !?

HTML Code: