I think this is what you are trying to do I hope it helps.
try changing fields to invisible, then in the change event of DDL
if (this.rawValue == "1"){
textBox1.presence = "visible"
textBox2.presence = "visible"
textBox3.presence = "invisible"
textBox4.presence = "invisible"
}else if (this.rawValue == "2"){
textBox1.presence = "invisible"
textBox2.presence = "invisible"
textBox3.presence = "visible"
textBox4.presence = "visible"
}