Pine Tree Literacy Foundation, a tax$-$exempt $501($c$)(3)$ organization, operates a bookstore on campus that sells new and used books. In addition to educational materials, the bookstore sells school merchandise and snacks to students and the public. All profits from the bookstore are used to fund the foundation$$s literacy outreach programs.

Which of the following best describes the foundation$$s bookstore activity for purposes of the unrelated business income tax $($UBIT$)?$

Group of answer choices

The bookstore income is entirely excluded from UBI because it supports the organization$$s exempt purpose.

All bookstore income is UBI because it involves commercial activity.

The bookstore income is exempt from UBI because the organization is a $501($c$)(3)$ charity.

The bookstore income is partially UBI$$sales of educational books are related to the exempt purpose, but sales of snacks and merchandise may be unrelated.