21、When you cut your skin，you blood（流血）．If a person loses a lot of blood，he will become ill and may die．Blood is very important．People have always known that．At one time in history, some people even drank blood to make them strong!

    When doctors understand how blood goes around inside the body, they try ways of giving blood to people who need it．They take blood from the healthy people and give it to people who need it．This is called“blood transfusion”．The blood goes from the arm of the healthy person to the arm of the sick people．

    But there are two problems．First，it does not always work．Sometimes people die when they have blood transfusion．Later, doctors found out that we do not have the same type of blood．There are four groups-O，A，B and AB．we all have blood of one of these groups．They also found they could give any kind of blood to people belonging to AB-groups．But they found that they must give A-·group blood to A-·group people and B·-group blood to B-group people．If I have O-group blood，then I could give blood to anyone else safely．

    There is another problem．To give blood of the right kind，doctors have to find a person of the right blood group．Often they can not find a person in time．If they have a way to keep the blood until someone needs it，they can always have the right kind of blood．At first they found they could keep it in bottles for fifteen to twenty days．They did this by making the blood very cold．Then they had ways to keep it longer．In the end they found a way of keeping blood for a long time．

    We call a place where we can keep money a“bank”．We call a place where we keep blood a“blood bank”．One day，when you grow up，you may give some of your blood to a “blood bank”．In this way you may stop someone from dying．Or perhaps one day you may become ill．You may need blood．Then the“blood bank”will give you the blood from another person．

1．From the passage，we learn that sometimes people die when they have blood transfusions because they __________．

A．are unhealthy people                             B．have lots of blood

C．are not given the right type of blood              D．are AB-group people

2．Which of the following is TRUE?

A．Doctors can give any kind of blood to the sick people．

B．Doctors can give any kind of blood to AB-group people．

C．Doctors can give any kind of blood to O-group people．

D．A O-group person can’t give his blood to a B-group person．

3．People set up the“blood bank”so that they can __________．

A．give the right kind of blood to the people who need it in time

B．keep different groups of blood as much as possible

C．make it easier to sell or buy blood

D．keep blood for more than twenty hundred years

4．From the last paragraph of the passage，we learn that __________．

A．the writer thinks it's good to give blood to a“blood bank”

B．we may become ill if we give blood to a“blood bank”

C．many people died because they lost lots of blood

D．there are three groups of blood