  <option>siblings(X, Y)</option>
              <option>parent_child(X, Y)</option>
              <option>father_child(X, Y)</option>
              <option>mother_child(X, Y)</option>
          </select>
      </div>
      <div>
          <input id="query" type="text" placeholder="Query">
      </div>
      <div>
          <button id="ask-btn">Ask</button>
          <button id="next-btn" disabled>Next</button>
          <button id="stop-btn" disabled>Stop</button>
          <button id="abort-btn" disabled>A