Final answer:
The sequences coding for transcription are most likely to be the most similar across major kingdoms because transcription is a fundamental and highly conserved biological process.
Step-by-step explanation:
The sequences coding for transcription would be expected to be the most similar when examining DNA from a representative species of each of the major kingdoms. Transcription is a fundamental process where DNA is copied into RNA, and because it is essential for all forms of life, the mechanisms and related sequences are highly conserved across different species. Proteins involved in protein degradation can also be diverse due to the specificity of these proteins for different organisms.
Cytochrome c oxidase, mentioned as a highly conserved protein in the question, is an example of a protein involved in a process (electron transport chain in cellular respiration) that is critical to life and therefore tends to show high similarity in the DNA sequences that code for it, reflecting the similarity seen in core processes like transcription.