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问题 单项选择题

以下不是电子显微镜镜筒必须具有真空的原因（）

A.防止气体电离和放电现象

B.防止电子枪灯丝被氧化

C.防止高速电子与分子碰撞而散射降低成像衬度以及污染样品

D.增加透明度

答案

参考答案：D

阅读理解

     Each year about thirteen million babies are born too soon. More than one million of them die as a
result of their prematurity(早熟). Yet experts say many early births can be prevented.
     The report came from the March of Dimes and the World Health Organization.Christopher Howson
is the vice president for global programs at the March of Dimes, a nonprofit group. He says there are a
number of simple, lowcost interventions that can improve the chances of a fullterm birth.
     CHRISTOPHER HOWSON: "We should treat malnutrition(营养不良)in women both before and
doing pregnancy. We should treat infections that increase risk. We should monitor pregnancies carefully
for signs of trouble. And should that baby be born preterm, we should care for that baby by providing a
package of interventions that have been shown to be tried and very effective."
     For example, there are programs in Africa that teach the skintoskin method, also known as kangaroo
care. Mothers learn to carry preterm babies in front instead the traditional African way of carrying a baby,
on the mother's back. Skintoskin helps keep a preterm baby warm. The direct contact also makes it
easier for the baby to breastfeed.
     Most preterm births take place in Africa and Asia.But rates in the United States have increased by
more than onethird in the last twentyfive years. This is largely the result of more births in older women
and more use of fertility treatments.
     Alan Fleischman is the medical director of the March of Dimes. He was among a group of medical
experts who met in Washington, D.C., earlier this month. The group met to develop a quality
improvement plan for dealing with the problem in the United States. Doctor Fleischman says there is
concern especially about rising numbers of what are known as late preterm births.
     ALAN FLEISCHMAN: "Those are the babies who are born between thirtyfour and thirtyseven
weeks gestation. Those are the fastest increasing numbers of prematures. In fact, they are responsible
for seventytwo percent of all prematures in America."
     The rise of these births may be linked to increased use of drugs to start or speed up labor and more
births by cesarean section. Doctor Fleischman says the group strongly advises against these interventions
before thirtynine weeks unless medically necessary.
     The experts also say doctors need to work with pregnant women to do a better job of estimating
exactly when a pregnancy began.

                               The problemOver one million of babies__1__their lives to prematurity
each year
                  __2__of  premature birthLack of__3__ ?Being infected
More births in older women
More people__4__fertility treatments
__5__use of drugs
__6__to be taken  to prevent  premature birthTreat malnutrition
Treat__7__increasing risk
Monitor pregnancies for signs of trouble
__8__after the preterm babies 
                           Experts'__9__ Many early births can be__10__ 
Doctors need to work with pregnant women
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单项选择题

乳牙根管消毒剂

A．氧化锌丁香油糊剂
B．氧化锌丁香油糊剂和牙胶尖
C．三氧化二砷
D．金属砷
E．甲醛甲酚
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