单项选择题

根据下列材料请回答 37～41 题：U.S.Life Expectancy Hits New High
Life expectancy rates in the United States are at an all—time high，with people born in 2005 projected to live for nearly 78 years，a new federal study finds.
The finding reflects a continuing trend of increasing life expectancy that began in1955.when the average American lived to be 59.6 years olD.By 1995，life expectancy was 75.8 years，and by 2005，it had risen to 77.9 years，according to the report released Wednesday.
“This is good news，”said report co—author Donna Hoyert，a health scientist at the National Center for Health Statistics.“It's even better news that it is a continuation of trends，so it is a long period of continuing improvement.”
Despite the upward trend，the United States still has a lower life expectancy than some 40 other countries，according to the U.S.Census(人口普查)Bureau.the country with the longest life expectancy is Andorra at 83.5 years，followed by Japan，Macau，San Marino and SingaporE.
Much of the increase owes to declining death rates from the three leading causes of death in the country—heart diseasE.6an'ceF arid strokE.
In addition，in 2005，the U.S.death rate dropped to an all—time low of less than 800 deaths per 1 00,000.
Dr.David Katz，director of the Prevention Research Center at Yale University School of Medicine，said，“News that life expectancy is increasing is，of course，gooD.But the evidence we have suggests that there is more chronic disease than ever in the U.S.”
Adding years to life is a good thing，Katz saiD.“But adding vital life to years is at least equally important.If we care about living well，and not just longer，we still have our work cut out for U.S.” he saiD.
第37题：Since 1955，life expectancy rates in the U.S.have
A.moved up and down.
B.been declining.
C.been on the risE.
D.remained steady.