title: Multiline string with added text from variables
body: <p>I am aware this will work:</p>
  
  <pre><code>string multiline_text = @"this is a multiline text
  this is line 1
  this is line 2
  this is line 3";
  </code></pre>
  
  <p>How can I make the following work:</p>
  
  <pre><code>string a1 = " line number one";
  string a2 = " line number two";
  string a3 = " line number three";
  
  string multiline_text = @"this is a multiline text
  this is " + a1 + " 
  this is " + a2 + " 
  this is " + a3 + ";
  </code></pre>
  
  <p>Is it possible without splitting the string into several substring, one for each line?</p>