In addition to pregnant women, fetuses, and neonates, another subpart of the HHS regulations provides additional protections for which of the following vulnerable populations? Prisoners. The elderly. Adults with decisional impairments. College students.

The correct answer is "Prisioners". The HHS regulations, 45 CFR part 46, include four subparts, two of which established the vulnerable populations that it aims to provide additional protection. Subpart B mentions the ones stated in the question, while subpart C mentions prisioners as other vulnerable population that HSS regulations offers additional protection.