1. Passage ThirteenTrees are useful to man in three important ways: they provide him with wood and other products; they give him shade; and they help to prevent droughts and floods.Unfortunately， in many parts of the world， man has not realized that the third of these services is the most important.In his eagerness to make money from trees， he has cut them down in large numbers， only to find that without them he has lost the best friends he had.And besides， he is usually too careless to plant and look after new trees.So the forests slowly disappear.This does not only mean that man will have fewer trees.The results are even more serious: for where there are trees， their roots break up soil——allowing the rain to sink in——and also bind the soil， thus preventing it from being washed away easily; but where there are no trees， the rain falls on hard ground and flows away， causing floods and carrying away the rich topsoil.When all the topsoil is gone， nothing remains but worthless desert.Two thousand years ago a rich and powerful country cut down its trees to build warships， with which to gain itself an empire.It set up the empire but， without its trees， its soil became poor and it grew weak.When the empire fell into pieces， there is nothing left except floods and starvation.What is the most important service of trees to man according to the passage?

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1. Passage Thirty-ThreeWe all know that DNA has the ability to identify individuals but， because it is inherited， there are also regions of the DNA strand which can relate an individual to his or her family (immediate and extended)， tribal group and even an entire population.Molecular Genealogy (宗谱学)can use this unique identification provided by the genetic markers to link people together into family trees.Pedigrees (家谱)based on such genetic markers can mean a breakthrough for family trees where information is incomplete or missing due to adoption， illegitimacy or lack of records.There are many communities and populations which have lost precious records due to tragic events such as the fire in the Irish courts during Civil War in 1921 or American slaves for whom many records were never kept in the first place.The main objective of the Molecular Genealogy Research Group is to build a database containing over 100，000 DNA samples from individuals all over the world.These individuals will have provided a pedigree chart of at least four generations and a small blood sample.Once the database has enough samples to represent the world genetic make-up， it will eventually help in solving many issues regarding genealogies that could not be done by relying only on traditional written records.Theoretically， any individual will someday be able to trace his or her family origins through this database.In the meantime， as the database is being created， molecular genealogy can already verify possible or suspected relationships between individuals.“For example， if two men sharing the same last name believe that they are related， but no written record proves this relationship， we can verify this possibility by collecting a sample of DNA from both and looking for common markers (in this case we can look primarily at the Y chromosome (染色体)，” explains Ugo Perego， a member of the BYU Molecular Genealogy research team.People in a large area may possess the same DNA thread because ().

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32. Questions 31 to 35 are based on the following passage.The United States is facing a housing crisis: Affordable housing is inadequate， while luxury homes abound (充裕)， and homelessness remains a persistent problem.Despite this， popular culture and the housing industry market happiness as living with both more space and more amenities (便利设施).Big houses are advertized as a reward for hard work and diligence， turning housing from a basic necessity into a luxury.This is reflected in our homes.The average single-family home built in the United States before 1970 was less than 1，500 square feet in size.By 2016， the average size of a new， single-family home was 2，422 square feet.What’s more， homes built in the 2000s were more likely than earlier models to have more of all types of spaces: bedrooms， bathrooms， living rooms， dining rooms， recreation rooms and garages.There are consequences of living big.As middle-class houses have grown larger， two things have happened.First， large houses take time to maintain， so cleaners and other low-wage service workers are required to keep these houses in order.Second， once-public spaces， where people from diverse backgrounds used to come together， have increasingly become privatized， leading to a reduction in the number of public facilities available to all， and a reduced quality of life for many.Take swimming pools.While in 1950， only 2，500 U.S.families owned pools， by 1999 this number was 4 million.At the same time， public municipal pools were often closed， leaving low-income people nowhere to swim.The trend for bigger housing thus poses ethical questions.Should Americans accept a system in which the middle and upper classes enjoy a luxurious lifestyle， using the low-wage labor of others? Are we willing to accept a system in which an increase in amenities purchased by the affluent means a reduction in amenities for the poor?I believe neither is acceptable.We must change the way we think: living well does not need to mean having more private spaces; instead， it could mean having more public spaces.A better goal than building bigger houses for some is to create more publicly accessible spaces and amenities for all.What is one of the consequences of living big?

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13.I don＇t mind ()the decision as long as it is not too late.

A、　you to delay making

B、　your delaying making

C、　your delaying to make

D、　you delay to make

答案：B