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问题 单项选择题

能形成气溶胶，不仅刺激动物机体产生不良反应，也是各种病原微生物的载体，人类变态反应的变应元的环境因素是（）。

A.风速

B.氨浓度

C.饲养密度

D.粉尘

答案

参考答案：D

多选题
如图为理想变压器原线圈所接交流电压的波形．原、副线圈匝数比n1：n2=10：1，串联在原线圈电路中电流表的示数为1A，下列说法正确的是（　　）

A．变压器输出端所接电压表的示数为20V

B．变压器的输出功率为200W

C．变压器输出端的交流电的频率为50Hz

D．穿过变压器铁芯的磁通量变化率的最大值为20/n2Wb/s
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单项选择题

Passage oneLong bus rides are like television shows .They have a beginning ,a Middle and an end –with commercials thrown in every three or four minutes .The commercials are unavoidable .They happen whether you want them or not .Every couple of minutes a billboard glides by outside the bus window . “buy super clean toothpaste”. “Drink Good’n Wet Root Beer .””Fill up with Pacific Gas .”Only if you sleep ,which site equal to turning the television set off ,are you spared the unending cry of “You Need It ! Buy It Now !” The beginning of the ride is comfortable and somewhat exciting ,Even if you’ve traveled that way before .usually some things have changed-new houses ,new buildings ,sometimes even a new road .The bus driver has a style of driving and it’s fun to try to figure it out the first hour or so . If the driver is particularly reckless or daring ,the ride can be an thrilling as a suspense story .Will the driver pass the truck in time Will the driver move into the right or the left –hand lane After a while,of course,the excitement dies down .sleeping for a while helps pass the middle hours of the ride .Food always makes bus rides more interesting .But you’ve got to be careful of what kind of foodyou eat .Too much salty food can make you very thirsty between stops. The end of the ride is somewhat like the beginning .You know it will soon be over and there’s a kind of expectation and excitement in that .The seat ,of course ,has become harder as the hours have passed.By now you’ve sat with you legs crossed ,with your hands crossed behind your head .the end comes just at the right time . There are just no more ways to sit.

The writer thinks that the end of the ride is somewhat like the beginning because both are ( )

A．exciting

B．comfortable

C． tiring

D．boring

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