radio button - adobe acrobat

You can tick a specific radio button by setting the field's value to its "Radio button choice".
For example, if the value is "1" and the name of the field is "RadioButton1", you can do it like this:

this.getField("RadioButton1").value = "1";

To make it dependent on the value of the drop-down you can use the following as the custom validation script of the drop-down field:

if (event.value=="AVILA") this.getField("RadioButton1").value = "1";
else if (event.value=="MADRID") this.getField("RadioButton1").value = "2";
else if (event.value=="TOLEDO") this.getField("RadioButton1").value = "3";
else this.getField("RadioButton1").value = "Off"; // the default value when nothing is selected