单项选择题

Some birds like to sit on a sheep because ______.

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

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热门试题

单项选择题

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

A．comfort
B．light
C．food
D．oxygen

单项选择题

What does second paragraph mainly discuss

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.