pdf form: Linking several fields so that one only shows when a certain selection is made in another

I have created a drop down field named STATUS with three options, R, Y or G. I have created a traffic light of 3 radio buttons with background and fill colours red, yellow and green. I would like to set the form up so that the red radio button shows automatically when R is selected in the STATUS field, the yellow radio button shows when Y is selected, and so on. I am new to Javascript and so far have been unable to work it out. Can anybody help me? Thanks!