Final answer:
In dendrochronology, scientists determine the age of a tree by examining the secondary xylem tissue in the tree trunk. The activity of the vascular cambium creates annual growth rings, and their characteristics can reveal the tree's age and past climatic conditions. The correct answer is d) Vascular cambium.
Step-by-step explanation:
When determining the age of a tree through dendrochronology, scientists are looking at the secondary xylem tissue of the tree trunk.
The activity of the vascular cambium creates annual growth rings, with the early wood formed during the spring having larger internal diameter and thinner cell walls, and the late wood formed during the fall having thicker cell walls.
By examining the number of annual rings and their characteristics, such as size and cell wall thickness, scientists can determine the age of a tree and the prevailing climatic conditions during each season.
Therefore, the correct answer is d) Vascular cambium.