Which of the following organisms multiply by fragmentation?

The correct option is All of the above.

Explanation:
Fragmentation is a form of asexual reproduction where the body of a multicellular organism breaks into two or more fragments, and each fragment subsequently develops into a complete, new organism.

Let us analyze the given options:
1. Fungi: Many multicellular fungi, such as molds and yeasts, can reproduce asexually by the fragmentation of their hyphae (tubular filaments).
2. Filamentous algae: Algae like Spirogyra consist of long filaments. When these filaments break into smaller pieces, each piece grows into a new filament through cell division.
3. Planaria: Planaria are flatworms known for their high regenerative capacity. If a planarian is cut or broken into pieces, each piece can regenerate the missing body parts to form a complete individual (often described as fragmentation followed by regeneration).

Since fungi, filamentous algae, and planaria are all capable of multiplying by fragmentation, the correct answer is indeed "All of the above".