Final answer:
The characteristic shared by all modern living systems is codons based on a triplet code, reflecting a nearly universal genetic code and indicating a common evolutionary history. Therefore correct option is C
Step-by-step explanation:
The characteristic shared by all modern living systems is C. Codons based on a triplet code. This is a key feature of the genetic code, which is nearly universal across all known living organisms, indicating a common evolutionary history. All living organisms, regardless of whether they are simple bacteria or complex multicellular organisms like humans, use a similar genetic code where sets of three nucleotides, known as codons, correspond to specific amino acids during the process of protein synthesis. This aspect of biology reflects one of the many conserved core processes that have evolved over time and are widely distributed among organisms today.