单项选择题
A．Animals. B．Plants. C．Both animals and plants. D．All living things.
A．One kind of animals is eaten up. B．One kind of plants is destroyed. C．One kind of animals eats another. D．One of the links is destroyed.
A．Each plant can live alone. B．Each animal can live alone. C．Everything living on earth cannot live without needing other living things. D．If living things want to live they must kill each other.