onchange event in javavscript

Question

<asp:DropDownList ID="Course" runat="server" class="slectbig" onchange="return ChnagePlaces()">

<asp:ListItem Value="0 " Selected="True">Select Course</asp:ListItem>

<asp:ListItem Value="1">B.Tech</asp:ListItem>

<asp:ListItem Value="2">Polytechnic</asp:ListItem>

<asp:ListItem Value="3">MBA</asp:ListItem>

</asp:DropDownList>

<asp:DropDownList ID="ACan" runat="server" class="slectbig" >

<asp:ListItem Value="0" Selected="True"> Select </asp:ListItem>

<asp:ListItem Value="1">Appearing In Class 10th</asp:ListItem>

<asp:ListItem Value="2">Appearing In Class 12th</asp:ListItem>

<asp:ListItem Value="3">Appearing In Graduation</asp:ListItem>

</asp:DropDownList>

<asp:TextBox ID="tenthper" runat="server" placeholder="10th %" > </asp:TextBox>

<asp:TextBox ID="twelthper" runat="server" placeholder="12th %" ></asp:TextBox> <asp:TextBox ID="gradutionper" runat="server" placeholder="gradution %" ></asp:TextBox>

 

i m just start code in javascript soo i hv many confusion.. if i select B.tech in Course ID then show list item Appearing In Class 12th and tenthper id and other listitem and control hide.... how to do code in javascript.... i have no idea about this...

 

plz help me...