title: sparqle query for capitols of all US's states
body: <p>I am trying to make a sparqle query for the capitols of all US's states. What is wrong with my sparqle query? It keeps failing.</p>
  
  <pre><code># Find US states, their capitals and largest cities
  PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;
  PREFIX rdf: &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#&gt;
  PREFIX rdfs: &lt;http://www.w3.org/2000/01/rdf-schema#&gt;
  PREFIX dbpr: &lt;http://dbpedia.org/resource/&gt;
  PREFIX dbpo: &lt;http://dbpedia.org/ontology/&gt;
  PREFIX dbpprop: &lt;http://dbpedia.org/property/&gt;
  
  #for all the capitols in the states
  SELECT ?capitol
  WHERE {
  ?capitol dbpo:state ?country .
  { ?capitol a dbpo:capitol } .
  { ?country a dbpprop:country "U.S." } .
  }
  </code></pre>