Final answer:
The adaptive radiation of eutherians began around 100 million years ago and continues to the present, corresponding with option C.
Step-by-step explanation:
According to the provided information regarding the history of life on Earth and the evolution of mammals, the adaptive radiation of eutherians, which are placental mammals, occurred within a specific time frame in the Earth's history.
The mammalian 'supertree' indicates that eutherians started diversifying as early as 95 million years ago, suggesting the correct time frame for this radiation would be from then until the present. Thus, the adaptive radiation of eutherians began around 100 million years ago and continues to the present which corresponds with option C.
This radiation is thought to have intensified particularly after the extinction of the non-avian dinosaurs about 65 million years ago, which likely provided evolutionary opportunities leading to the explosion of diversity within this group.
So Option C.