how to activate a textbox if I select an other option in drop down box

Question

suppose I\'ve a 3 options in a drop down box say red , blue, others. If a user select option as an others then below a text box should be visible to wrtie his own favour

Answer 1

As Umesh Patil answer have comment say that there is problem. I try to edit answer and get reject. And get suggest to post new answer. This code should solve problem they have (Shashi Roy, Gaven, John Higgins).

 
  
 


   
    pick a color  
    RED
    BLUE
    others