Explanation:

Your NCERT says that when choosing flowers to study, avoid using marigold, chrysanthemum or sunflower. This is because they are not single flowers, but, groups of flowers.
In those species that have more than one flower on an axis, the collective cluster of flowers is termed an inflorescence.
Some inflorescences are composed of many small flowers arranged in a formation that resembles a single flower.
The common example of this is most members of the very large composite (Asteraceae) group. A single daisy or sunflower, for example, is not a flower but a flower head—an inflorescence composed of numerous flowers (or florets).
An inflorescence may include