Which of the following is an example of an exempt organization that may be subject to unrelated business income tax?

An animal shelter that sells donated pet supplies.

A horticultural center that rents office space in its annex. No significant personal services are provided to tenants, and the annex was not debt-financed.

A literary magazine that sells advertising space to local businesses.

A hospital gift shop that sells stuffed animals and balloons intended to be given to patients as gifts.