We learn from the text that corals depend on plants for ____________.

A．Some animals and plants depend on each other for existence.
B．Some animals and plants develop their relationship easily.
C．Some plants depend on each other for food.
D．Some animals live better together.

A．they can eat its parasites
B．they enjoy travelling with the sheep
C．they depend on the sheep for existence
D．they find the position most comfortable