(a) (i) Vegetative propagation by stem (it) Budding (iii) Regeneration.
(b) FragmentatioiTis a asexual method of reproduction in which an organism simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals.
Spirogyra is the multicellular organism with relatively simple body organisation which reproduces through this simple method of reproduction, i.e., fragmentation.