Final answer:
The 2008 WSF panel entitled '90 is the New 50: The Science of' focuses on the science of longevity. Longevity pertains to a protracted existence or a long lifespan, and it is an essential topic in gerontology.
Step-by-step explanation:
The subject of the 2008 WSF panel entitled "90 is the New 50: The Science of" refers to the concept of longevity, which is an option (a). Longevity is the term used to describe a protracted existence or a lengthy lifespan. The field of gerontology, which is concerned with aging and the processes associated with it, often focuses on how to increase the health span and life span of individuals
When talking about the aging process, which is the main focus of this WSF panel, it's also helpful to understand thanatology, which is the study of death and dying (option c from your provided information). However, the specific term directly associated with the panel's subject is longevity.
In a different context, such as environmental science, the term residence time is used to refer to the average time a molecule spends in its reservoir, which is not related to this panel's subject but is another concept crucial to understanding certain processes in the world around us.