Final answer:
The 5' region of human genes predominantly contains promoters and enhancers, which are crucial for the initiation and regulation of transcription.
Step-by-step explanation:
The types of sequences located in the 5′ region of human genes are primarily promoters and enhancers. The promoter is where the preinitiation complex binds to initiate transcription, which is a crucial step in gene expression. Enhancers are sequences that can increase the transcriptional activity of a gene. While introns and exons are part of the gene structure, and splice signals are involved in mRNA processing, neither are specific to the 5' region. Moreover, start and stop codons are part of the coding sequence, not typically located at the 5' region. Similarly, polyadenylation sequences are found at the 3' end of the gene, responsible for the addition of a poly-A tail to mRNA. Therefore, the correct answer is C Promoters and enhancers.