Panel Visibility Problem!

I am making a project in which i databinded dropdownlist which contains two options and I created two pannels containg more controls.
When option 1 is chosen pannel 1 becomes visible and when option 2 is chosen pannel 2 becomes visible.(This is Suppose to happen)
When i run it and i choose option 2 it works perfectly whereas when i choose option 1 both the panels appear.
 I have set their visibility as false and written this code behind
protected void dropdownsource_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (dropdownsource.SelectedValue == "Air")
            Panel1.Visible = true;
        Panel2.Visible = false;
          
        if (drop ...