Most animals only have animals of a different kind for food. But sometimes two kinds of animals come together in a partnership which is good for them. You may have noticed some birds on the backs of sheep. This is not because they want a ride, but because they find easy food in the parasites on sheep. The sheep let the birds do so because they can stop the parasites from troubling them. So though they can do with it by themselves, they can do better together with each other.  

Sometimes an animal has a plant partner. The relationship develops until the two partners cannot do without each other. This is so in corals of the sea. Inside their bodies they have very small plants, which act as “cleaners”, taking the useless things from the coral and giving oxygen in return. That is what the animal needs to live. If the plants are killed, or are even kept from receiving light so that they cannot live as usual, the corals will die. 

Reading Comprehension:

1.Some birds like to sit on a sheep because ________. 

A. they can eat its parasites             B. they enjoy traveling with the sheep 

C. they can’t live without its parasites   D. they want to find the warm place

2. The underlined word “they” in the first paragraph means _________.

A. birds and parasites    B. birds and sheep  

C. parasites and sheep    D. birds, parasites and sheep 

3. We learn from the passage that corals need plants for _______.

A. friends    B. light    C. food    D. oxygen 

4.The Chinese for the word “oxygen” is _________.

A. 氧气      B. 空气    C. 废气     D.二氧化碳

5.What is the second paragraph mainly about? 

A. Some animals and plants cannot live without each other.

B. Some animals and plants cannot develop their friendship easily.

C. Some plants eat each other.     

D. Some animals live better together.

Key:

1A  2B  3D  4A  5 A

Background Information:

寄居蟹与海葵共生。海葵固着在寄居蟹所寄居的螺壳上，通过寄居蟹的运动而扩大其取食范围，反过来寄居蟹可以海葵的刺细胞来防御敌害。
白蚁与鞭毛虫共生又是一个典型的例子。白蚁的肠道为鞭毛虫提供了生活场所，而鞭毛虫可以帮助白蚁消化其所赖以生存的纤维。
爬行动物中的“绿毛龟”与丝状藻类之间是共生现象的另一种形式，丝状藻借龟甲表面，作为附生的基底，从龟甲表层分泌物中吸取养料而滋生；当整个龟甲被丝状藻覆盖后，形似龟甲长满绿毛从而可逃避敌害。
燕千鸟，它充当了“牙签”，又叫“牙签鸟”。 鳄鱼一吃东西，牙缝里就嵌进了肉屑残质，慢慢地腐败生蛆。燕千鸟在鳄鱼的稀稀落落的牙齿中间走来走去，剔牙齿，捉蛆虫，侍候得鳄鱼舒舒服服。同时，它自己也饱餐了一顿。
世界上还有一种小鸟，和老虎是好朋友，它总是跟随在老虎的左右飞来飞去。当老虎张开大嘴休息时，这些“小家伙”就肆无忌惮地飞进老虎口，也同样啄食牙缝中的肉屑，成了猛虎的“朋友”。 老虎对这种小鸟非常友好，从不吞吃它。这种小鸟名叫虎雀。

Vocabulary:

partnership 伙伴关系

parasites 寄生虫

Coral 珊瑚

Oxygen 氧气