private void Form1_KeyDown(object sender,KeyEventArgs e)
{  if(e.Alt&&e.KeyCode==Keys.Delete)
      {删除用户选定的项}

}

private void listBox1_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.Alt && e.KeyCode == Keys.Delete)
            {
                listBox1.Items.Remove(listBox1.SelectedItem);
                listBox1.SelectedIndex = 0;
            }
        }

------解决方案--------------------

  if(e.Alt&&e.KeyCode==Keys.Delete)
    ListBox1.Items.Remove(ListBox1.SelectedItem);
或
while (listBox1.SelectedItems.Count != 0)
           {
               listBox1.Items.RemoveAt(listBox1.SelectedIndices[0]);
           }