单项选择题

10kV及以下变配电所，采用( )直流操作电源时，宜采用直流电源成套装置。直流成套装置宜配套采用阀控密封铅酸蓄电池和高频开关充电模块。

A.10V或110V
B.220V或110V
C.220V或10V
D.10V或380V

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Cultural DifferencesPeople from different cultures sometimes do things that make each other uncomfortablE.sometimes without realizing it. Most Americans______1 out of the country and have very______2 experience with foreigners. But they are usually spontaneous．friendly and open．and enjoy______3 new peoplE.having guests and bringing people together formally or informally．They tend to use first names______4 most situations and speak freely about themselves. So if your American hosts do something that______5 you uncomfortablE.try to let them know how you feel. Most people will______6 your honesty and try not to make you uncomfortable again. And you'll all______7 something about another culture!Many travelers find______8 easier to meet people in the U. S. than in other countries. They may just come up and introduce themselves or even invite you over______9 they really know you. Sometimes Americans are said to be______10 . Perhaps it seems so．but they are probably just______11 a good timE.Just like anywhere elsE.it takes time to become real friends______12 people in the U.S..If and when you______13 American friends．they will probably______14 introducing you to their friends and family．and if they seem proud______15 you．it's probably because they arE.Relax and enjoy it.第 51 题请选择（1）处的最佳答案．A.have never beenB.have been neverC.has never beenD.has been never

A.sometimes
B.friendly
C.and
D.having
E.They
F.try
G.but
H.it
I.S..
J.they
K.and
L.it's
M.
A.have
N.have
O.has
P.has

单项选择题

变压器的铁损又称为空载损耗，其大小与铁芯材质有关，与负荷电流( )。

A.成正比
B.成反比
C.无关
D.平方成正比

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