The correct answer is B. Fragmentation.

Explanation: 
Spirogyra is a filamentous green algae that reproduces vegetatively by fragmentation. In fragmentation, the filaments of Spirogyra break into smaller pieces, each of which grows into a new filament. This is a form of asexual reproduction, as no gametes or spores are involved. Binary fission and multiple fission are forms of cell division seen in unicellular organisms like bacteria and protozoans. Spore production is a mode of reproduction in fungi, algae, and some plants.