title: Angular 4 setting selected option in Dropdown
body: <p>There are several questions about this and different answers but none of them really answers the question. So again:</p>
  <p>Setting default of a Dropdown select by value isn't working in my case. Why?
  This is from the dynamic Form tutorial of Angular 4:</p>
  <pre><code>&lt;select [id]=&quot;question.key&quot; [formControlName]=&quot;question.key&quot;&gt;
        &lt;option *ngFor=&quot;let opt of question.options&quot; [value]=&quot;opt.key&quot; [selected]=&quot;opt.selected&quot;&gt;{{opt.selected+opt.value}}&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  <p>It doesn't select anything. Available options are:</p>
  <ul>
  <li>trueaaa</li>
  <li>falsebbb</li>
  <li>falseccc</li>
  </ul>
  <p>But static true:</p>
  <pre><code>&lt;option ... [selected]=&quot;true&quot;&gt;...&lt;/option&gt;
  </code></pre>
  <p>selects the last value (all true).
  It also works with a private variable <code>boolvar = true</code> and using it in <code>[selected]=&quot;boolvar&quot;</code></p>
  <p>I don't understand the difference between the &quot;opt&quot; object and the class variable.</p>