2nd Dropdown is not saving data.

I have a select list in a metabox which value is saved successfully after clicking "Update" when editing post. Of course, the values are custom taxonomies. But i don't know how to add another select list and make it save its values successfully too...

PHP Code:

---

add_action( 'add_meta_boxes', 'so_custom_meta_box' );

function so_custom_meta_box($post){
add_meta_box('so_meta_box', 'Reproductor 1', 'custom_element_grid_class_meta_box',     $post->post_type, 'normal' 

, 'high');
}

add_action('save_post', 'so_save_metabox');

function so_save_metabox(){ 
global $post;

if(isset($_POST["custom_element_grid_class"])){
     //UPDATE: 
    $meta_element_class = $_POST['custom_element_grid_class'];
    //END OF UPDATE

    update_post_meta($post->ID, 'custom_element_grid_class_meta_box',   $meta_element_class);
    //print_r($_POST);
}
}

function custom_element_grid_class_meta_box($post){
$meta_element_class = get_post_meta($post->ID, 'custom_element_grid_class_meta_box', true); ?>   

  <select name="custom_element_grid_class" id="custom_element_grid_class">
  <option value="Netu" <?php selected( $meta_element_class, 'Netu' ); ?>>Netu</option>
  <option value="Netu-latino" <?php selected( $meta_element_class, 'Netu-latino' ); ? >>Netu Latino</option>
  <option value="Netu-castellano" <?php selected( $meta_element_class, 'Netu- castellano' ); ?>>Netu Castellano</option>
  <option value="Netu-vose" <?php selected( $meta_element_class, 'Netu-vose' ); ?>>Netu    Vose</option>
</select>

  <select name="custom_element_grid_class" id="custom_element_grid_class">
  <option value="Vk" <?php selected( $meta_element_class, 'Vk' ); ?>>Vk</option>
  <option value="Vk-latino" <?php selected( $meta_element_class, 'Vk-latino' ); ?>>Vk  Latino</option>
  <option value="Vk-castellano" <?php selected( $meta_element_class, 'Vk-castellano' );  ?>>Vk Castellano</option>
  <option value="Vk-vose" <?php selected( $meta_element_class, 'Vk-vose' ); ?>>Vk    Vose</option>
</select>

<?php
}

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Only the first select list values are saved when i click update, but not the second. I already know this has to be with the save code but i can't figure out how to be able to modify it so i can put a second select list and its value can be saved.