Step 1: Understanding the Concept:
In flower arrangements and the cut-flower industry, "filler" plants are used to fill spaces between large, showy focal flowers.
These plants provide structure, background contrast, and bulk to bouquets and vases.
Step 2: Detailed Explanation:
Let us analyze the listed flower crops:
1. Nasturtium:
This is a trailing annual grown primarily for its colorful edible flowers and round, peltate leaves.
It is not used as a standard commercial cut-flower filler.
Thus, Option (A) is incorrect.
2. Rose, Carnation:
These are major, high-value focal flowers in floral designs due to their large size, distinct form, and striking colors.
They are not used as fillers.
Thus, Options (B) and (D) are incorrect.
3. Gypsophila (Baby's Breath):
This annual (or perennial) plant produces dense, branching stems covered in thousands of tiny white (or pink) flowers.
It is the most famous and widely used "filler" crop in the florist trade.
Its delicate, cloud-like texture is used to fill the empty spaces between larger focal flowers like roses or carnations.
Step 3: Final Answer:
The annual flower crop used as a filler is Gypsophila.
This matches Option (C).