Rule: Unrelated business income is:

1. Derived from an activity that constitutes a trade or business,

2. Is regularly carried on, and

3. Is not substantially related to the organization's tax-exempt purpose.

Note: An unrelated business does not include any activity where all the work is performed for the organization by unpaid volunteers. Thus, using unpaid volunteers makes that business or activity "related." Choice "B" is correct. The sale of a trade association of publications used as course materials for the association's seminars, which are oriented towards its members, will not result in unrelated business income.Choices "d", "a", and "c" are incorrect, per the above explanation.