阅读下列短文, 从每小题所给的A、B、C、D四个选项中, 选出最佳选项.

    For too many, the damage begins early in life. Four out of 10 babies born in the United States do not form a strong relationship with either parent, and they will pay for that the rest of their lives.

    New research from Princeton University confirms what other researchers have already found: The number of babies born into families that are too poorly equipped(装备、配备) to give them a fair chance of having a successful life is very big.

    That finding is supported by many other research Projects, including a study from the University of Rochester showing that nearly one-third of U.S. parents don't know what to expect from their new horns, or how to help them grow and learn and get along with others. Babies, as others have pointed out, don't come with an owner's manual.

    The basic problem, according to the Princeton study, is 40 percent of infants in the U.S. live in fear or distrust of their parents, and that will turn into aggressiveness（侵犯）, defiance（挑衅） and hyperactivity（多动） as they grow into adults.

    Of that number, 25 percent don't have a close relationship with their parents because the parents don't satisfy their needs. And 15 percent find their parents so troubling that they will avoid them whenever possible.

    That will not necessarily result in a lifetime of violence(暴力), but it will make living a successful life much more difficult.

"They can overcome(克服) it," sociologist (社会科学家) Sophie Moullin of Princeton, lead author(作者) of that study, said in a telephone interview. "It's not a make or break situation, but they might find it harder to control their behavior."

    Moullin, along with coauthors from Columbia University and the University of Bristol in England, analyzed(分析) more than 100 research projects, to reach their conclusions.

    There are many factors, including poverty(贫穷), ignorance（无知）, and stress among parents who are so busy with their own problems that a new child is sometimes more than they can deal with.

    Yet strong relationships, the researchers say, are amazingly simple to achieve.

已知一次函数$f\left(x\right)=kx+b$的图像经过点$P\left(1,2\right)$和$Q\left(-2,-4\right)$，令$a_n=f\left(n\right)f\left(n+1\right),n\in N^{*}$，记数列$\left\{\frac{1}{a_n}\right\}$的前项和为$S_n$，当$S_n=\frac{6}{25}$时，$n$的值等于（   ）

“齐国君王齐桓公，任用丞相叫管仲，‘尊王攘夷’为口号，第一霸主逞威风”。该歌谣所反映的历史时期是（    ）