All dropdownlist resets at single selectedIndexchange
<p>i have this project am working on the registration form has four dropdownlist .two are been populated at page load event from the database </p>

<pre><code>        if (!IsPostBack)
        {

            if (!getState()) { return; }
            if (!GetFaculty()) { return; }

        }
</code></pre>

<p>the rest two are been populated at the selectIndexchange of the two (state and faculty)</p>

<pre><code>  protected void ddlFaculty_OnSelectedIndexChanged(object sender, EventArgs e)
  {
        if (Page.IsPostBack) 
        { 
            try
            {
                string sqltext = @"Select Name from Department where FacultyID=" + this.ddlFaculty.SelectedValue.ToString();
                List&lt;Department&gt; mlist = new List&lt;Department&gt;();
                mlist = ServiceProvider.Instance().GetDepartmentService().GetDepartment_GetDepartment(sqltext);
                if (mlist.IsNullOrEmpty()) { return; }
                this.ddlDepartment.DataSource = mlist;
                this.ddlDepartment.DataTextField = "Name";
                this.ddlDepartment.DataValueField = "DepartmentID";
                this.ddlDepartment.DataBind();
                this.ddlDepartment.Items.Insert(0, new ListItem("--Select Department--", "0"));

            }
            catch (Exception ex) { return; }
        }

    }

    protected void ddstate_OnSelectedIndexChanged(object sender, EventArgs e)
    {
        if (Page.IsPostBack)
        { 

            try
            {
                string sqltext = @"Select Name from University where StateID=" + this.ddlState.SelectedValue.ToString();
                List&lt;University&gt; mlist = new List&lt;University&gt;();
                mlist = ServiceProvider.Instance().GetUniversityService().GetUniversity_UniversityName(sqltext);
                this.dDUniversity.DataSource = mlist;
                this.dDUniversity.DataTextField = "Name";
                this.dDUniversity.DataValueField = "UniversityID";
                this.dDUniversity.DataBind();
                this.dDUniversity.Items.Insert(0, new ListItem("-- Select University--", "0"));
                this.dDUniversity.SelectedIndex = 0;

            }
            catch (Exception ex) { return; };
        }
    }
</code></pre>

<p>the problem now is that once i select a value from the selectedIndexChanged of the ddstate in ddUniversity it works fine , then selecting value from the selectedIndexChanged of the ddfaculty from the ddDepartment will automatically reset the ddUniversity and also clicking the signup button equally rests every thing in the ddUniversity and ddDepartment.
this my html code</p>
