对于直径较大，断面不平整宜采用对焊的工艺为（）。

Inthepast,operationsweredifficult.Untilthemiddleoftheeighteenfifties,surgerywasverydangerous.Manypatientsdiedaftereventhesmallestoperations.Thiswasbecausebacteriaenteredthecutsinthepatientsbodied’andstartedinfection.Insomecountries,upto90percentofpatientsdiedfrominfectionafteroperations.In1865,however,JosephLister,aBritishsurgeon,foundananswertotheproblem.Heusedan“antisepticduring”andafteroperations.Thiskilledthedangerousbacteriaandmostofhispatientslived.Sincethen,surgeonshaveusedantisepticsinalloperations.SurgeryhasdevelopedinmanyimportantwayssincethedayofJosephLister.Today,whenpatientsgotohospitalforanoperation,theycanexpectthebesttreatment,incleanandhygienicconditions.

33.Operationsweredifficultanddangerousuntil_______.

A.1850

B.themiddleof1850

C.themiddleofthefiftiesoftheeighteenthcentury

D.themiddleofthefiftiesofthenineteenthcentury

34.Inthepassage,surgerymeans__________.

A.Theperformingofanoperation

B.cure

C.treatment

D.medicine

35.Inthepast,upto90percentofpatientsdiedafteroperationsmainlyb

ecause__________.

A.bacteriaenteredthecutsinthepatientsbodies’andinfectiontookplace

B.theconditionsinhospitalswerebad

C.theskillofsurgeonswasnotsogood

D.therewerenogoodmedicineatthattime

36.Whichtopicofthefollowingbestsuitsthepassage?

A.Operationsweredifficultinthepast

B.ThedevotionofJosephListertomedicalscience

C.Surgeryhasbecomesafer

D.Developmentsinsurgery

37.JosephListerwas________.

A.aFrenchman

B.aGerman

C.anEnglishman

D.anAmeric

在使用GIF方式优化图象时，以下描述不正确的是：

下面选项中对色阶描述正确的是：

下面哪些命令具有还原操作的作用