Answer:
The correct answer would be - the 16S rRNA gene.
Step-by-step explanation:
16S ribosomal RNA is a small subunit of ribosomes found in prokaryotic cells such as microbes. It is coded by the 16S rRNA gene that is used in constructing phylogenies again due to the slow rate of evolution.
This gene is suggested to be used as a molecular clock that is more reliable as it has sequences that show similar functionalities in distantly related bacterial lineages. It is the gene that produces protein more quickly than other bacteria.