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【单选题】
下列说法正确的个数有( )个 1设函数 的两个混合偏导数 存在,则一定相等; 2设函数 的两个混合偏导数 存在,则当二者连续时一定相等; 3设函数 在点 的某邻域中有定义,若 处连续,则 在点 处连续; 4若 都不存在,则 在点 处不连续; 5若 都存在,则 在点 处连续;
A.
1个
B.
2个
C.
3个
D.
4个
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http://leicloud.ulearning.cn/course/mediacontent/20130911/lesson-09/audio/toeic_ch08_07_04_02a.mp3
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【单选题】Usually the panels are interlocked with _____ so that the devices can be made dead before the doors are opened.
A.
protective earth
B.
isolators
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【简答题】A．Just before Columbus left. B．Just after Columbus left. C．Two hundred years before Columbus left. D．After 1300.
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【单选题】There will be great demand on your efforts before you reach the ______ of the race.
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dead line
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【单选题】Do you sell light bulbs here?
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【单选题】I'm Hardy. _____ to meet you. [     ]
A.
Like
B.
Happy
C.
Nice
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【单选题】Usually the panels are interlocked with _____ so that the devices can be made dead before the doors are opened.
A.
protective earth
B.
isolators
C.
ground switch
D.
circuit-breakers
查看完整题目与答案
【单选题】听力原文：W: I've been around the whole store, but I couldn't find any sixty-watt bulbs. Don't you carry them anymore? M: Oh, they used to be on Aisle 12, but we've moved them. Now you'll find them at the ...
A.
Toilet bowl cleanser.
B.
Household goods.
C.
Light bulbs.
D.
Tulips.
查看完整题目与答案