19．A.Salesmen B．Checkers

　　C．Humans D．Machines

　　20．A.make B．lack

　　C．contribute D．limit

　　Ⅲ.阅读理解

　　Scientists have discovered that tea contains high levels of compounds that help to reduce the amount of fat absorbed by the gut (内脏) and can cut cholesterol (胆固醇). However, proteins found in cows' milk prevent this fat­fighting ability.

　　New research has shown that the compounds, called theaflavins and thearubigins, prevent obesity when given to rats that were also on a high­fat diet. The researchers now believe this could explain why people in Britain appear not to benefit from the healthy effects of tea despite being among the world's biggest consumers of the beverage.

　　Dr Devajit Borthakur, a scientist at the Tea Research Association, in Jorhat, India said, "When tea is taken with milk, theaflavins and thearubigins form complexes with the milk protein, which causes them to precipitate (沉淀)"．

　　Scientists at the research center are now working on developing new kinds of tea with higher levels of these compounds, which are known as polyphenols, while also looking for ways of making them less influenced by milk.

　　A study by scientists in Japan, which was published this month in the journal of Nutrition, reveals that extracts from tea leaves prevent the absorption of fat in the gut of rats fed with high­fat diets. These rats also had less fat tissue on their bodies and lower fat content in their livers.

　　Dr Hiroaki Yajima, a scientist with the Kirin Beverage Company in Japan who carried out the Japanese research, said, "Black tea extracts may prevent obesity because of eating too much by preventing intestinal lipid (肠脂) absorption."

　　The fermentation (发酵) process used to make "black" tea leaves, the most commonly drunk type of tea in the UK, has also been found to boost levels of these fat­fighting compounds compared to green tea, which is unfermented.

　　The research suggests that despite more attention being paid to the health benefits of green tea, black tea may have better effects on our health which are reduced by the tendency to drink it with milk.

1．We can learn from the passage that proteins found in cows' milk ________.