title: Add text from 2 listBox to one listBox
body: <p>How can I add items from 2 listBox to one listBox?</p>
  
  <p>ex: listBox1 contain Hello listBox2 contain World! So if button1 is clicked in listbox3 will display Hello World! side bye side but not in a new line like</p>
  
  <p>Hello</p>
  
  <p>World!</p>
  
  <pre><code>private void button2_Click(object sender, EventArgs e)
  {
    listBox3.Items.Add(listBox1.Items + listBox2.Items);
  }
  </code></pre>