Multiple combi (visible/hidden)

Hello,

I got a problem with combi form. I want to create few combi forms where depending on selected value from previosu combi the rest is vissible or hidden.

For example:

combobox1 value = a, b or c

if combobox1 = a

then show combox2,

combobox 3 and 4 hidden

if combox1 = b

then show combobox3,

combobox 2 and 4 hidden

Any ideas how to do that?