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    American researchers say drinking tea may help strengthen the body's defense system against infection£®Doctors at Brigham and Women's Hospital in Boston£¬ Massachusetts£¬ did the study£® The team studied a chemical found in black£¬ green£¬ oolong and pekoe tea£® This chemical is an amino acid called L-theanine£® The scientists say it may increase the strength of gamma delta T cells£® That's the letter T£¬ not the drink£® Gamma delta T cells are part of the body's defense£®

First£¬ the researchers mixed some of these cells with antigens found in the amino acid£® Antigens help the body react to infection£® Then the scientists added some bacteria£® Within twenty-four hours£¬ the cells produced a lot of interferon£¬ a substance that fights infection£® Cells not mixed with the antigens did not produce interferon£®

In the second part of the study£¬ eleven people drank five to six cups of black tea every day£® Ten other people drank the same amount of instant coffee£® That is dried coffee mixed with hot water£®

Two weeks later£¬ and again two weeks after that£¬ the researchers tested the blood of all twenty-one people£® They also looked at what happened when they added bacteria to the blood cells£® They found that the tea drinkers produced five times more interferon after they started drinking tea£® The coffee drinkers did not produce interferon£®

Doctor Jack Bukowski led the study£® He says the antigens added to the gamma delta T cells were responsible for the increased reaction to the bacteria£® He says that the study also showed that the cells were able to remember the bacteria and fight them again the next time£®

Earlier research already has found that tea can help prevent heart disease and cancer£® Doctor Bukowski says the new study must be repeated by more people£® "If the findings prove to be true£¬" he says£¬ "then tea drinking might also help protect against bacterial infections£®" He says the amino acid L-theanine could be removed from the tea and used as a drug to strengthen the body's defenses£®

21£®We may know from the text that ______ can be found in different kinds of tea£®

A£®L-theanine                           B£®Gamma delta T cells

C£®interferon                           D£®bacteria

22£®Tea may help strengthen the body's defense system because it helps ______ £®

A£®to add some bacteria to the blood cells

B£®the body to produce more gamma delta T cells

C£®the body to produce more interferon

D£®to mix antigens with some of the cells in the body

23£®According to Dr Bukowski£¬ ______ £®

A£®the findings of the study have already proved to be true

B£®further study is needed to prove the findings true

C£®he has taken some amino acid L-theanine from tea and made a drug with it

D£®he is not sure whether tea help prevent heart disease and cancer