Bootstrap and Webform – Select Options getting the options into columns

Can anyone point me to a simple solution to get the list items into columns by applying something like col-md-4 – so in this case the items would be in three columns as seen on a desktop screen. I’d assumed that there might be a way through the settings in webform to add a class to the individual item but no… or am I missing something?

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Source: https://www.drupal.org/taxonomy/term/3/feed