Two scientists in California now think they can find out a person’s real age.Jeffery Bada and Patricia s do chemical tests on teeth.When we are born the amino acids（氨基酸）in our teeth are in one form.Then，as we grow older these amino acids change into a second form.Every year，one thousandth of the amino acids changed.So，by testing just one tooth and counting the number of amino acids in each form，Bada and s can work out a person’s age.They tested a tooth from the body of an Eskimo（爱斯基摩人）woman who died 1 600 years ago.From the appearance of her body，she was between 50 and 60 years old when she died.The tooth test put her age at 53.Then the Russian Government sent them a tooth from an old man in Georgia.The tooth said she was 99.Her real age was 96.The Russians are now hoping to send more teeth，from the very old people without birth certificates（出生证明书）.But there are problems.Some of the centenarians（百岁老人）have lost all their teeth.The others want to keep their teeth until they drop out naturally.So the Russian Government and the American scientists have to wait and hope.
61.Jeffery Bada and Patricia s believe that they can tell a person’s age according to_______.
A.an experiment on his bone
B.the shape and condition of his teeth
C.a test on the amino acids within his body
D.the changing form of amino acids in his teeth
62.According to the passage，which of the following statements is true?
A.The amino acids in an ’s teeth may differ from those in a baby’s.
B.The number of amino acids in a 20-year-old man is different from that when he was seven.
C.Amino acids in one teeth changes without affecting their forms.
D.Scientists no w can tell how long a person will live by testing his teeth.
63.Why are the two scientists asked to find out some very old Russians’ age?
A.Because the Government wants to know how long these old people can live.
B.Because they have no birth certificates.
C.Be cause people who have tooth problems tend to live longer.
D.Because the Government wants to know their dates of birth and death.
.In order to find out the exact age of some people over 100，both the Russian Government and American scientists_______.
A.should wait until all of them die
B.should pull out one of their teeth
C.have to wait for their teeth to drop out naturally
D.want to have their teeth pulled out
65.The central idea of the passage is_______.
A.the relationship between people’s teeth and ages
B.the relationship between amino acids and teeth
C.the contradiction（矛盾）between scientists and patients
D.the contradiction between the Government and the scientists