Which of the following is an example of secondary growth?
increase in length
increase in thickness or girth
increase in root hairs
increase in leaf number

The correct answer is B. Increase in thickness or girth

Explanation:

In plants, there are mainly two types of growth that can take place, these are primary and secondary growth. Primary growth mainly takes place in the stems and roots especially in the tips of these and because of this, this type of growth is the one that occurs when a plant increase in length or there is an increase in its roots. On the other hand, secondary growth occurs in the stem mainly as this increases in thickness. Considering this, the one that is an example of secondary growth is the increase in thickness or girth (circumference).