将4至12的九个整数填入下图九个格内，使纵、横及斜三个数字的和均是一样，问A和B是那两个数字？

等差数列$\left\{a_n\right\}$前n项和为$S_n$，满足$S_{20}=S_{40}$，则下列结论中正确的是（  ）

漫画《躲风头》告诉我们（    ）

①市场调节具有盲目性和滞后性

②必须规范市场秩序，强调诚实守信

③发挥宏观调控在资源配置中的决定性作用

④市场需要法律、道德的规范和引导

根据短文理解，从A、B、C、D四个选项中选择正确答案填空。

    When learning new vocabulary, don't just memorize list of words. 1, try to make five sentences using each new word. Then use the new word as you can the first day you learn it. This way you will remember new words 2 longer.

    Practicing sounds, you know, is difficult—the “th” sound for example. Choose words that 3“th” and repeat them over and over again until you are comfortable with them. Let's try! This, that, those, them, think, thought, through, thin, thick.

    Read, read, read— in English, of course! Reading is one of 4 ways to increase your vocabulary and 5 your grammar in a natural and fun way. Be sure to choose topics or books you are interested in.

    When someone 6 in English, listen for the main point. If you 7 a word you don't understand, ignore (忽略) 8 and go on listening. If you stop and think about the word, you will miss 9 the person is saying.

    Always remember—Practice 10 perfect.

若$a_i,b_i\in R_{+}\left(i=1,2,3,...,n\right)$  ，求证$\left(a_1{b}_1+···+a_n{b}_n\right)\left(\frac{a_1}{b_1}+···+\frac{a_n}{b_n}\right)\ge {\left(a_1+···+a_n\right)}^2$  .