title: In which cases a method call succeeds?
body: <p>In the Ruby expression <code>a.foo</code>, which calls method <code>foo</code> on receiver <code>a</code>, which of the following conditions affects whether the call succeeds?</p>
  
  <ol>
  <li><code>a</code> responds to the foo method.</li>
  <li><code>a</code>'s class, or one of its superclasses or included modules, implements method_missing in a way that handles the foo method.</li>
  <li><code>a</code> is an instance of a class, rather than the class itself.</li>
  <li><code>a</code> has the correct type.</li>
  </ol>