问题 多选题

物体受三个共点力作用做匀速直线运动,已知其中两个力的大小分别是F1=4N.F2=7N,则第3个力F3的大小不可能是(  )

A.1N

B.7N

C.11N

D.15N

答案

两个力的合力的最大值为 F1+F2,最小值为|F1-F2|,第三个力只要在这两个力范围内,三个力的合力就可能为零,

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阅读理解

阅读理解。

Dear Friend,

     The recent success of children' s books has made the general public aware that there' s a huge market out

there.

     And there's a growing need for new writers trained to create the $ 3 billion worth of children' s books

bought each year...plus stories and articles needed by over 650 publishers of magazines for children and

teenagers.

      Who are these needed writers? They' re ordinary folks like you and me.

                                                              But Am I Good Enough?

      I was once where you might be now. My thoughts of writing had been pushed down by self-doubt, and I

didn't know where to turn for help.

     Then, I accepted a free offer from the Institute to test my writing aptitude(潜能), and it turned out to be the

inspiration I needed. 

                                                              The Promise That Paid Off

     The Institute made the same promise to me that they will make to you, if you show basic writing ability:

     You will complete at least one manuscript (手稿) suitable to hand in to a publisher by the time you finish

our course.

      I really didn' t expect any publication before I finished the course, but that happened, I sold three stories.

And I soon discovered that was not unusual at the Institute.

     Since graduation, I have authored 34 nationally published children' s books and over 300 stories and articles.              

                                                                      Free Test and Brochure

     We offer a free aptitude test and will send you a copy of our brochure describing our recognized homestudy courses on the basis of one-on-one training.

     Realize your writing dream today. There' s nothing sadder than a dream delayed until it fades forever.

                                                                                               Sincerely,

                                                                                      Kristi Holl, Instructor .

                                                                                  Institute of Children' s Literature

1. From the first three paragraphs, we learn that _______.

A. children' s books are usually bestsellers

B. publishers are making $3 billion each year

C. magazines for teenagers have drawn public attention

D. there is a growing need for writers of children' s books

2. When finishing the course, you are promised to _____.

A. be a successful publisher

B. become a confident editor

C. finish one work for publication

D. get one story or article published

3. Kristi Holl mentions her experience mainly to____.

A. prove she is a good instructor

B. promote the writing program

C. give her advice on course preparation

D. show she sold more stories than articles

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