Final answer:
The age of a twig is determined by counting the number of apical bud scar rings. Dendrochronology uses secondary xylem rings in a tree trunk to ascertain age and climate conditions.
Therefore, options A is correct.
Step-by-step explanation:
The age of a twig can be determined by looking at the number of apical bud scar rings. These rings form each year as the twig grows and the terminal, or apical, bud forms new leaves and stem tissue before leaving behind a scar from the previous year's growth. By counting these scars, which form a ring around the stem, one can determine the number of growth seasons the twig has undergone, which correlates with its age.
Dendrochronology, which is a method used to date the age of a tree, relies on examining the annual rings in the tree trunk, specifically the secondary xylem. These rings represent the increase in thickness or girth of the tree each year and are influenced by environmental conditions, giving clues not just to the age but also to the historical climate.