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单项选择题

You create a Microsoft ASP.NET application by using the Microsoft .NET Framework version 3.5. You write the following code fragment:  
<asp:ListBox SelectionMode="Multiple" ID="ListBox1" runat="server"> 
</asp:ListBox>  
<asp:ListBox ID="ListBox2" runat="server"> 
</asp:ListBox>  
<asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />   
You need to ensure that when you click the Button1 control, a selected list of items move from the ListBox1 control to the ListBox2 control. 
Which code segment should you use?()

A.A
B.B
C.C
D.D

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单项选择题You create a Microsoft ASP.NET application by using the Microsoft .NET Framework version 3.5. You create two user controls named UserCtrlA.ascx and UserCtrlB.ascx. The user controls postback to the server.  You create a new Web page that has the following ASPX code:   <asp:CheckBox ID= Chk  runat= server      oncheckedchanged= Chk_CheckedChanged     AutoPostBack= true   >   <asp:PlaceHolder ID= PlHolder  runat= server >< asp:PlaceHolder>   To dynamically create the user controls, you write the following code segment for the Web page:  public void LoadControls()  {  if (ViewState[ CtrlA ] != null)  {  Control c;  if ((bool)ViewState[ CtrlA ] == true)  {  c = LoadControl( UserCtrlA.ascx );  } else {  c = LoadControl( UserCtrlB.ascx );  }   c.ID =  Ctrl ;  PlHolder.Controls.Add(c);  }  }   protected void Chk_CheckedChanged(object sender, EventArgs e)  {  ViewState[ CtrlA ] = Chk.Checked; PlHolder.Controls.Clear();  LoadControls();  }   You need to ensure that the user control that is displayed meets the following requirements: It is recreated during postback It retains its state.   Which method should you add to the Web page?()

A.A
B.B
C.C
D.D