low search form

{exp:low_search:form result_page="{pre_res}" form_class="form-horizontal"}
<div class="form-group">
<label class="control-label col-md-3" for="writer_title">Name</label>
<div class="col-md-6">
<input type="text" class="form-control" id="writer_title" name="search:title" maxlength="100">
</div>
</div>

<div class="form-group">
<label class="control-label col-md-3">County</label>
<div class="col-md-6">
<select class="form-control" name="category:county">
    <option value="">All</option>
    {exp:channel:categories category_group="6" style="linear" show_empty="no" disable="category_fields" channel="wis"}
      <option value="{category_id}">
        {category_name}
      </option>
    {/exp:channel:categories}
  </select>
</div>
</div>

<div class="form-group major">
<label class="control-label col-md-3">Genres</label>
<div class="col-md-13"><div class="row">
{exp:channel:categories category_group="4" style="linear" show_empty="no" disable="category_fields" channel="wis"}
    <div class="checkbox col-md-8">
    <label>
      <input type="checkbox" name="category:genre[]" value="{category_id}">
      {category_name}
    </label>
    </div>
  {/exp:channel:categories}
</div></div>
</div>

<div class="form-group major">
<label class="control-label col-md-3">Sessions</label>
<div class="col-md-13"><div class="row">
  {exp:channel:categories category_group="5" style="linear" show_empty="no" disable="category_fields" channel="wis"}
  <div class="checkbox col-md-8">
    <label>
      <input type="checkbox" name="category:session[]" value="{category_id}">
      {category_name}
    </label>
    </div>
  {/exp:channel:categories}
</div></div>
</div>

<div class="form-group major">
<label class="control-label col-md-3">Age Groups</label>
<div class="col-md-13"><div class="row">
  {exp:channel:categories category_group="11" style="linear" show_empty="no" disable="category_fields" channel="wis"}
    <div class="checkbox col-md-3">
    <label>
      <input type="checkbox" name="category:age[]" value="{category_id}">
      {category_name}
    </label>
    </div>
  {/exp:channel:categories}
  </div></div>
</div>

<div class="form-group actions">
<div class="col-md-13 col-md-offset-3">
<button type="submit" class="button">Search</button>
</div>
</div>
{/exp:low_search:form}