Genes that control factors such as size, color and shape determine the differences in fruit. And now that scientists have discovered how to detect different genes, farmers can hand over a young and tender branch to have its genes checked prior to planting. It works the same way as a detective checking fingerprints. Once farmers know which trees are good and which are bad, they can discard the bad ones. Farmers can even create new varieties according to their individual tastes.In the past three years, tens of thousands of tests were carded out to determine the genetic (基因的) features 0f fruit. Zhang, a Chinese scientist, showed a photo of a DNA-test and pointed to the shining lines on it, saying thatthe lines were genetic signs that tell us what a tree's fruit will be like. For example, the ordinary pear tree bears fruit after four years. But now it only takes a month to test the DNA from a young leaf and a farmer will know everything about its fruit. By mixing different types of trees with suitable genes, farmers can create whatever fruit trees they want.21.Detecting different genes in plants is like（）.A.the examination of human finger-printsB. the development of new varieties of fruitC.the checking of young a nd tender branchesD.the distinction between bad trees a nd good ones23.We learn from the first paragaph that the study of genes.（）A. has greatly affected fruit outputB. has been a popular planting procedureC. will change the taste of individualsD. will play a vital role in fruit production24.Now famers can tll whether afruit tee is dsirable or notby（）.A. having a DNA test of a young leaf of the teeB. mixing dferet types of sitble genesC.checking its young branches before pantingD. comparing the sining ines with the geneic signs .25. The ps el us thet he new geneic echoy wi enble ames.（）A. increase the DNA ofa fuit treeB. improve the qualty of fruitC. make use of the sing feturesof fuitD. change the cycle of fuit production