Three dropdown lists

I have script to change 2nd dropdown list based on seletion on the 1st drodownlist. I need to add 3rd dropdown list that would also change based on 1st dropdown list selection. Please help. Thanks in advance

topmostSubform.Page1.DropDownList2::exit - (JavaScript, client)

if     (this.rawValue == 1)

{

    this.parent.DropDownList4.selectedIndex = 0;

}

else

{

this.parent.DropDownList4.rawValue = "";