The correct answer is (C) Fragmentation and regeneration.
Spirogyra reproduces by fragmentation (breaks into pieces that grow into new individuals), and Planaria reproduces by regeneration.
The textbook (Chapter 7) explicitly states that Spirogyra "simply breaks up into smaller pieces upon maturation" — this is fragmentation. Planaria is the classic example of regeneration (cut pieces regrow into complete organisms). Students often confuse the two; remember: fragmentation = organism breaks apart naturally; regeneration = lost/cut parts regrow. Option C is the only one with this correct order.