如图所示,A、B两球完全相同,质量均为m,用两根等长的细线,悬挂在升降机的天花板上的

题型:单项选择题

问题:

如图所示,A、B两球完全相同,质量均为m,用两根等长的细线,悬挂在升降机的天花板上的O点,两球之间连着一根劲度系数为k的轻质弹簧。当升降机以加速度a竖直向上加速运动时,两根细线之间的夹角为θ。则弹簧的长度与原长相比缩短了()

A.

B.

C.

D.

考点:高中物理弹力弹力题库
题型:单项选择题

某受体被激动后,引起支气管平滑肌松弛,此受体为

A.α受体

B.β1受体

C.β2受体

D.M受体

E.N2受体

题型:单项选择题

适用单元化装载以及大量或保管周期短的货品应该采用的货位编码方式是 ( )。

A.区段方式

B.货品类别方式

C.地址式

D.坐标式

题型:单项选择题

下列描述中属于物质的化学性质的是(______)属于化学变化的是(C)

A.胆矾是蓝色的固体

B.硫在点燃条件下能燃烧

C.澄清石灰水中通入二氧化碳后变浑浊

D.玻璃破碎

题型:单项选择题

阅读理解。

    根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,选项中有两项为多

余选项。

     When I walked into the house after school, the first thing I noticed was a box with items I recognized

from my dad's office.  When he told me that he was laid off, I thought he was joking.  Then I noticed his

seriousness and realized he was telling the truth.  My father has always been a hard worker.  He has

prided himself on his career.    1   I guess I had taken his work for granted.  

      2   For starters, he was home all the time.  It meant my bed had to be made, my room cleaned up,

and my homework done right after school.  I would come home every day to find him at the computer

searching for jobs.   3   He seemed down, though he tried to be optimistic.  He asked my brother and me

to spend less.  I gave up my spending money, which wasn't much.  I also found a part-time job.  

      4   He explained that he never wanted to be laid off again, so he was going to start his own business.  Day by day, I watched him build it.  One evening I asked if he needed help.  "Only if it doesn't affect

school," he said.  I showed up at his office the next afternoon, and most afternoons after that for two

months.  

      5   The terrible experience for our family taught me how to deal with difficulties.  Now I know that

through creative problem-solving, I can always find Plan B.  I can ask for help and take risks.  What I

have learned from my dad's understanding of business and his work ethic(信条)are two of the most

important lessons I will ever learn.  And they will be my principles for success.  

    A.  Providing for our family has been his joy.  

    B.  I made every effort to solve his problems.  

    C.  I began to notice how losing his job had affected him.  

    D.  My father's unemployment created many changes in our lives.

    E.  After months of searching, my dad decided to go in a totally different direction.

    F.  His courage and determination helped him to become successful in his new career.  

    G.  I always knew he was a hard worker, but watching him in action influenced me a lot.

题型:单项选择题

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