The age of a tree can be calculated by _____.

The correct answer is Option (4) → Measuring the number of annual rings

In a tree trunk, a new layer of wood grows every year: light, wide wood in spring and dark, dense wood in autumn. Together they form one ring a year, so counting the annual rings on a cut trunk gives the age of the tree. This method is called dendrochronology.

Height, trunk thickness and width depend on the kind of tree, the soil and the rainfall, so two trees of the same size can be of very different ages.