No botanist lives long enough to study the complete life cycle of an individual California redwood tree. Nevertheless, by observing many trees at different stages, botanists can piece together the evolution of a single tree. Exactly the same principle applies in astronomy to the study of the life-story of globular clusters, huge spherical aggregations of about a million stars all swarming about each other.
Which of the following is an assumption made in the passage above
A．The methods of scientists in one field generally carry over to other fields even if the subject matter is vastly different.
B．Observations of the life cycle of a single individual have little value in scientific studies.
C．Globular clusters at different stages of development are accessible to astronomers for observation and study.
D．There are globular clusters that have not so far been detected by astronomers.
E．(E) Redwoods and globular clusters must both be studied intensively now, while they still exist in sufficient numbers.