医学考博公共英语模拟题三.pdf

中国考博辅导首选学校 医学考博公共英语模拟题三 Part IV. Reading Comprehensio (30%) Directions: I this part of the test there are six passages. Following each passage there are five questions with four choices. Choose the best answer and mark your answer o the ANSWER SHEET. Passage One Cells ca otremai alive outside certai limitsof temperature, andmuchnarrower limitsmark theboundariesofeffectivefunctioning. Enzyme (酶) systems of mammals and birds are most efficient only withi a narrow range around 37ºC; a departure of a few degrees from thisvalue seriouslyimpairstheirfunctioning.Eve thoughcellsca survivewider fluctuations, the integratedactions ofbodily systems are impaired. Other animals have a wider tolerance for changes of bodily temperature. Forcenturiesithasbee recognizedthatmammalsandbirdsdiffer from other animals i the way they regulate body temperatures. Ways of characterizing the difference have become more accurate and meaningful over time,but popular terminology stillreflects the old divisio into “warm-blooded’ and “cold-blooded” species; warm-blooded includedmammals andbirds,whereas allother creatures were consideredcold-blooded.Asmore specieswere studied,itbecame evident that this classificatio was inadequate. A fence lizard or a desert iguana (鬣蜥)—each cold-blooded—usually has a body temperature only a degree or two below that of humans and so is not 中国考博辅导首选学校 cold. Therefore the next distinctio was made betwee animals that maintai a constant body temperature, called homotherms(同温动物), and those whose body temperature varies with their environment, calledpoikilotherms(变温动物). But this classificatio also proved inadequate,because amongmammals therearemany thatvary theirbody temperaturesduringhibernation. Furthermore,many invertebrates(无 脊椎动物) that live i the depths of the ocea never experience a change i the chill of