Final answer:
HOTAIR performs as both a scaffold and a guide, thus the correct answer is D, both B and C. It serves as a structural platform for protein complexes and directs these complexes to target genes.
Step-by-step explanation:
The function that HOTAIR performs is both a scaffold and a guide. This means that the correct answer to the given question is option D, both B and C. HOTAIR, which stands for HOX Transcript Antisense Intergenic RNA, is a long non-coding RNA molecule known to have regulatory roles in gene expression. It can serve as a scaffold by providing a structural platform for the assembly of multiple protein complexes such as Polycomb Repressive Complex 2 (PRC2).