题目内容
阅读下面短文,从每小题所给的A、B、C、D四个选项中选出最佳选项,并在答题卡上将该项涂黑。
Rats use their tails to help keep body temperature. The rat has specialised blood vessels which control the amount of blood flowing to its tail. Blood flowing into the furless skin of the tail carries heat which is then let out of the body. The rat can direct anywhere between 0.1 and 10 per cent of its cardiac output(心输出量) to the tail. Under ideal conditions, it can get rid of up to 20 per cent of its metabolic(代谢) heat in this way. On the other hand, controlling blood flow to the tail reduces heat loss in cold weather. It is interesting to note that the length of the rat's tail is partly determined by the temperature of the environment in which it is raised.
Observing my three rats suggests that the long tail-usually around the same length as the body-is used for balancing. Although rats cannot grasp objects with their tails, they do seem able to control the muscles along the tail's length with considerable precision(精确). If a rat is running along a narrow surface such as a rope, the tail constantly flicks from side to side to steady them.
When my rats are eating, they rest on the edge of the food bowl, which is about 20 centimetres from the floor of the cage, grasping the bowl with their back paws and eating with their front paws. In doing this their ends stick out quite a long way over the side of the bowl so that it looks as if they should fall off backwards.
As an experiment, I moved the food bowl to about 10 centimetres above the floor of the cage, which is about the length of a rat's tail. Now, instead of curling their tails under the bowl, the rats stretch out their tails and point them straight down so that they touch the floor, supporting their bodies with this “third leg”.
1.A rat's tail is useful in the way ________.
[ ]
A.of controlling the amount of blood flowing
B.to direct its cardiac output
C.of keeping balance and maintaining body temperature
D.to be used as another leg
2.What is true about the rat's tail according to the passage?
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A.The temperature of where the rat grows determines the length of its tail.
B.The tail is more or less as long as its body.
C.More blood will flow to the tail in cold winter weather to keep it warm.
D.It can get rid of 20% of its metabolic heat under any weather condition.
3.Which of the following has nothing to do with keeping balance?
[ ]
A.The tail flicks from side to side when a rat is running along a rope.
B.The tail sticks out quite a long way curling over the side of the bowl.
C.The tail stretches out straight down to touch the floor like a “third leg”.
D.The tail reduces the body temperature bay letting out heat from it.
4.Which one of the statements below is a wrong description?
[ ]
A.The rat uses fore and hind paws as well as its tail when eating in a bowl.
B.It's better to have the bowl 10 to 20 cm above the cage floor when feeding rats,
C.Rats sometimes uses their tails to grasp things they want.
D.Home-raised rats are more skilled at using their tails.