centers WP_QUERY

// WP_Query arguments
$args = array(
	'post_type'              => array( 'centers' ),
	'posts_per_page'         => '20',
	'meta_query'             => array(
		'relation' => 'OR',
		array(
			'key'     => 'mc_city',
		),
		array(
			'key'     => 'mc_state',
		),
		array(
			'key'     => 'mc_zipcode',
		),
	),
);

// The Query
$query = new WP_Query( $args );