title: collect all array items from each object
body: <p>I have 2 entities:</p>
  
  <pre><code>class A {
      ...
  }
  class B {
      IEnumerable&lt;B&gt; bs;
  }
  </code></pre>
  
  <p>I have array of A's and I need to get all the B's in one IEnumerable. I can do:</p>
  
  <pre><code>IEnumerable&lt;A&gt; as=....;
  
  IEnumerable&lt;IEnumerable&lt;B&gt;&gt; bss=as.Select(x=&gt;x.bs);
  
  IEnumerable&lt;B&gt; all=null;
  foreach (IEnumerable&lt;B&gt; bs is bss) {
      if (all==null) { all=bs; }
      else { all=all.Contact(bs); }
  }
  </code></pre>
  
  <p>I want to know if there is shorter way to do this.</p>
  
  <p>Thanks</p>