Asp.net using c# coding

Question

Dear All,             
                       (ASP.NET USING C# CODING)

        I designed one form with the following tools in ASP.NET:

         
         label 1(Select your branch)   Dropdownlist 1(Select,MCA,OR&CA)

          label 2(MCA)                                              label 3(OR&CA)
       
      Dropdownlist 2(Select,Sem1,sem2)               Dropdownlist 3(Select,sem1,sem2,sem3)   


here when i select my branch is MCA from DropDownlist1 then the label2 and dropdownlist2 must be visible and when i select my branch is OR&CA then the label 3 and dropdownlist3 must be invisible.

kindly send me codings for this yaar..
I will be very much thankfull to you..