Age of a tree can be known by counting its annual rings.

Answer

### Step-by-Step Solution:

1. **Understanding Annual Rings**: Trees exhibit growth in layers, known as annual rings. Each ring represents one year of growth.

2. **Types of Growth**: The growth of trees can be categorized into two types based on the seasons:
- **Spring Growth**: This is when the tree experiences rapid growth due to favorable conditions. The wood formed during this time is lighter in color and is referred to as the "spring wood" or "early wood."
- **Autumn Growth**: This occurs when growth slows down as conditions become less favorable. The wood formed during this period is darker and is known as "autumn wood" or "late wood."

3. **Counting the Rings**: Each year, a tree produces one light ring (spring wood) and one dark ring (autumn wood). By counting the total number of these rings, one can determine the age of the tree.

4. **Conclusion**: Therefore, the statement that the age of a tree can be known by counting its annual rings is true. Each pair of light and dark rings corresponds to one year of growth.