Final answer:
Life span is the maximum age a species member can reach, while life expectancy is the average age that individuals in a group can expect to live based on statistical data. These measures are often derived from life tables, which provide insightful demographics such as mortality rates and survival probabilities at different ages.
Step-by-step explanation:
The correct answer to the student's question is: B) Life expectancy; life span. Life span is the oldest possible age that members of a species can attain, while life expectancy is the average life span of individuals in a particular group. Life tables are used to gather such data, dividing a population into age groups and showing the probability of individuals dying at different ages, their mortality rate, and their life expectancy at each interval.
An example of this can be seen in a study of Dall mountain sheep, where life expectancy numbers are provided, revealing the statistical measure of the average length of life within that population. Factors such as genetics, environment, and healthcare practices can influence both life span and life expectancy.