我有一个情态范畴，在我的情态范畴中，我有三个子范畴。这是我的情态范畴的结构。

-Modal
  -Water Pumps
  -Water Heaters
  -Electrical

在这里，我只想从我的模态类别中的水泵子类别中获得一个帖子，并显示在模态中。这是我的代码，其中显示了所有类别名称为modal的，如何将其限制为类别名称modal和水泵的子类别

<div id="myModal38" class="modal fade" tabindex="-1">
<?php $args1 = array(
                    \'post_type\' => \'post\',
                    \'category_name\' => \'modal\',
                    \'posts_per_page\' => \'1\',
                );
    $modalPost = new WP_Query( $args1 );
    if( $modalPost->have_posts() ) : 
?>
    <div class="modal-dialog">
    <?php while ( $modalPost->have_posts() ) : $modalPost->the_post(); ?>
        <div class="modal-content">
            <div class="modal-header">
                <button class="close" type="button" data-dismiss="modal">×</button>
                    <h4 class="modal-title"><?php the_title(); ?></h4>
            </div>
            <div class="modal-body">
                <?php the_post_thumbnail(); ?>
                <?php the_content(); ?>
    <?php endwhile; ?>
            </div>
    <?php endif; ?>
    <?php wp_reset_postdata(); ?>       
            </div><!-- /.modal-content -->
    </div><!-- /.modal-dialog -->
</div><!-- /.modal -->
<!-- Modal -->

$idObj = get_category_by_slug(\'water-pumps-modal\'); 
$args1 = array(
    \'post_type\' => \'post\',
    /*\'category_name\' => \'modal\',*/
    \'category__in\' => array( $idObj->term_id ), // Take only IDs of the categories
    \'posts_per_page\' => \'1\',
);

\'tax_query\' => array(
                    array(
                        \'taxonomy\' => \'Category\',
                        \'field\'    => \'slug\',
                        \'terms\'    => array(\'Modal\' => \'water-pumps\')   
                        ),
                    ),
        );