Angular 4 setting selected option in Dropdown : <p>several questions about this and diffrent answeres. But none of them realy answeres the question. So again:</p>

<p>Setting default of a Dropdown select by value isnt working in my case. why?
This is from the dynamic Form tutorial of Angular 4:</p>

<pre><code>&lt;select [id]="question.key" [formControlName]="question.key"&gt;
      &lt;option *ngFor="let opt of question.options" [value]="opt.key" [selected]="opt.selected"&gt;{{opt.selected+opt.value}}&lt;/option&gt;
&lt;/select&gt;
</code></pre>

<p>It doesnt 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]="true"&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]="boolvar"</code></p>

<p>I dont understand the difference between the "opt" object and the class variable??</p>
