铁道的坡度是指铁道的两端点的标高差与水平距离()。A、之比 B、之积 C、之和 D、

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问题:

铁道的坡度是指铁道的两端点的标高差与水平距离()。

A、之比

B、之积

C、之和

D、之差

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题型:单项选择题

“10a>10b”是“lga>lgb”的(  )

A.充分不必要条件

B.必要不充分条件

C.充要条件

D.既不充分也不必要条件

题型:单项选择题

“渐减数”是指每个数字比其左边数字小的正整数(如98765),若把所有的五位渐减数按从小到大的顺序排列,则第20个数为(    )。

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两拉杆的材料和承受轴向拉力相同,且均处在弹性范围内,若两杆长度相同,横截面积A1>A2,则()。

A.

B.

C.

D.

题型:单项选择题

阅读理解。

     Did you know that birds could be "property owners", too? In spring, the male robin (知更鸟) looks for a

place to build a nest. A tree neara green lawn (草坪) that has many worms (虫子) suits him best. When he

finds the right place, he sings loudly. He tells other birds that this place is his property.

      At the same time, other birds are choosing places for their nests. A robin does not mind if swallows nest

nearby because swallows eat insects. They leave his worms alone. But other robins are different. They would

eat the worm supply he needs for his own family.

      When another male robin comes near, the robin owner sings to wam him away. The property owner looks

cross and fierce (凶猛的). He raises his head feathers and holds his tail high. If the owner cannot frighten

away the new robin, he attacks. The two fight until one is the winner. The new bird often gives up and flies

away. So the first bird has defended his property. He now has the right to build a nest in the place.

1. The male robin looks for a place to build a nest _____ .

A. near swallows

B. near other male robins

C. near a lawn with worms

D. in the woods

2. The story does not say so, but it makes you think that robins _____.

A. drive away all the other birds

B. do not care where they build their nests

C. are careful when choosing a place to nest

D. are not afraid of other birds

3. On the whole, this story is about _____.

A. what robins eat

B. robins finding a nesting place

C. robins finding friends

D. how robins live with swallows

4. Why does the male robin raise his head feathers and hold his tail high?

A. He wants to drive away another male robin.

B. He is getting ready to hunt for worms.

C. He is too warm.

D. He wants to look more beautiful.

5. In this passage the word "cross" means ______.

A. angry

B. worried

C. happy

D. around

题型:单项选择题

即使变压器运行电压过高也不会出现高次谐波。

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