Option D — they reproduce asexually.
Spirogyra reproduces by fragmentation, Leishmania by binary fission, and Hydra by budding — all asexual methods. Also, Leishmania is unicellular while Spirogyra and Hydra are multicellular, so options B and C are incorrect.
The question tests whether students can find the one common trait shared by all three organisms. Sexual reproduction is ruled out (all three examples in the chapter illustrate asexual reproduction). Options B and C are wrong because Leishmania is unicellular while Spirogyra and Hydra are multicellular. Option D is the only universally correct statement. Examiners award the mark for choosing D with a brief justification.