For example, the regular sale of pharmaceu- tical supplies to the general public by a hospital pharmacy does not lose its identity as a trade or business, even though the pharmacy also fur- nishes supplies to the hospital and patients of the hospital in accordance with its exempt pur- pose. Similarly, soliciting, selling, and publishing commercial advertising is a trade or business even though the advertising is published in an exempt organization's periodical that contains editorial matter related to the organization's ex- empt purpose