Fill in the blanks `:`
(i) Variability of animals `"….............."` has greatly helped in their classification.
(ii) Heterotrophic mode of nutrition is an important factor in causing great diversity in the `"…................"` of animal structure.
(iii) Fertilization results in the formation of `"..................."` zygote.
(iv) The digestive cavity of Hydra has only `"..............."` opening for both ingestion and egestion.
(v) Radial symmetry means that the body of the animal may be divided into `"..................."` equal halves.

Explanation

(i) Morphyology (ii) Gut or digestive system. (iii) Diploid (iv) Single ( mouth ) (v) Two.