The reproductive development process of frog is as follows: the male frog first calls to attract the female frog, and then the female frog hugs the male frog to promote the discharge of hermaphroditic germ cells. The hermaphroditic germ cells combine in water to form fertilized eggs. Many fertilized eggs form an egg mass together, and the fertilized eggs hatch into tadpoles. Tadpoles grow hind legs first, then front legs, and finally their tails gradually disappear and become young frogs, which gradually grow into frogs, that is, fertilized eggs, tadpoles, young frogs and adult frogs; Male frogs attract female frogs by singing their sacs, and male and female frogs embrace each other to promote the discharge of hermaphroditic germ cells, so the essence of mutual embrace is sperm discharge and ovulation. When sperm and egg cells are discharged at the same time, the probability of their meeting is greatly increased, so the significance of this process is to improve the fertilization rate. The chirping of male frogs is a reproductive behavior, which attracts frogs of the opposite sex.
So choose: C.