The correct answer is C. When two species separated from a shared ancestor
Step-by-step explanation:
In biology, the term "molecular clock" refers to a technique biologist use to study the origin of mutations that made one; species led to others. This implies through the molecular clock scientist can determine the evolution and species and the time in which two species separated from a shared ancestor or diverged. This technique relies mainly on biomolecular information based on sequences of DNA as differences in DNA between two species with a common ancestor marks the divergence of these species, also molecular clocks use the comparison of fossils to confirm evolutive divergence. Therefore, it can be concluded biologist use molecular clocks to try to measure "when two species separated from a shared ancestor".