The life cycle of stars is on the order of billions of years, much longer than a human life span or even the existence

The life cycle of stars is on the order of billions of years, much longer than a human life span or even the existence of astrophysics as a discipline. How do we understand the whole stellar life cycle? The Hertzsprung-Russell (HR) diagram sorts stars into different categories depending on their properties. Stellar clusters are collections of stars all the same age. The location of all the stars in a single stellar cluster on an HR diagram demonstrates the categories for stars at that particular age, and a comparison of plots on the HR diagram for multiple stellar clusters indicates how the different kinds of stars change over the course of their life cycles. The achievement is analogous to that of an imagined intelligent mayfly that, despite being alive for only a single day, is able to figure out the entire human life cycle by observing __________________.

Which of the following most logically completes the passage?
a. the students at a school that goes from kindergarten to the twelfth grade
b. a gathering of grandparents with their grandchildren
c. a college with reunions of all classes that graduated N years ago, where N is a multiple of five
d. the photos of a single living elderly individual, from early childhood to present day
e. a hospital with children and adult patients of all ages and a variety of conditions


OA C

Source: Magoosh