https://wordpress.stackexchange.com/questions/77052/creating-custom-field-with-drop-down-on-new-post-page
Saving a dropdown value in wordpress
https://stackoverflow.com/questions/8987218/saving-a-dropdown-value-in-wordpress
https://wordpress.org/support/topic/dropdown-select-custom-fields-in-registration/
https://ivetetecedor.com/how-to-use-a-drop-down-menu-for-wordpress-custom-fields/