诗歌赏析。

                                                                                                                                    青春之歌
                                                                                                                                      阮章競
                                                                                                                      每个人只能得到一次生命，
                                                                                                                      每一年，只有三个月是春天。
                                                                                                                      琴弦断了，可以续一千次，
                                                                                                                      但是青春之歌，
                                                                                                                       却唱不了十个十年！
                                                                                                                       珍贵的青春之歌呀，
                                                                                                                       应该骑上天马，凌空高唱，
                                                                                                                       不应该躺在软沙地上，
                                                                                                                       为空虚的幻想低吟。

                                                                                                                       不要等待这样一天：
                                                                                                                       沙漠已经结满苹果，
                                                                                                                        荒山已经崛起新城，
                                                                                                                         冰川开着白色的素馨；
                                                                                                                        在那个时候，你才拄着拐棍，
                                                                                                                         踏着青年时代朋友的脚印，
                                                                                                                         歇在他们手栽出来的树阴下，
                                                                                                                         才听到你这同时代的人，
                                                                                                                         那副衰老而又沙哑的声音。

                                                                                                                         不要过着这样的日子：
                                                                                                                         在戈壁，或在草原的公园里，
                                                                                                                          一群小鹰似的儿童向你起来：
                                                                                                                          “公公，哪个石阶是你砌的？”
                                                                                                                          在那个时候，你才“英勇”地说：
                                                                                                                           “当时我正在编写争待遇、
                                                                                                                           忙风雨、搞恋爱、闹情绪的喜剧，
                                                                                                                           耽误了坐上那次直达快车，
                                                                                                                           结果是老态龙钟才赶到这里。”

以下统计数据表明我国在人口方面存在的问题有(     )

注：第六次人口普查同第五次相比，65岁及以上人口（老年人口）的比重上升1.91%。
①我国人口增长速度总体上已呈下降趋势，人口总数下降   ②我国人口文化素质偏低
③我国的人口老龄化加快                                                           ④我国人口总量大 

长江三角洲地处我国沿海地区的中部，长江的入海口，是我国经济最发达地区。阅读材料，回答问题。

材料一：我国四大地理区域及长江三角洲图。

材料二：近代史上，上海成为第一批被迫开放的通商口岸之一，也是最早接触“外界”的地方。

材料三：（1937年）8月13日，日军大举进攻上海，妄图在三个月内灭亡中国。两国军队在上海及其周围地区展开长达三个月的激战。——摘自人教版《历史与社会》

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。

    Tired of traditional running? Well, maybe it's time to try using your hands instead. That's what Shaun McCarty and other Australians are doing — running on all fours. ____

    McCarthy, who comes from Melbourne, Australia, said he's the one behind the term “crunning.” “It's not crawling, it's not running.” he said. “Crunning is a better workout than running. It puts more of an emphasis（着重）on the body than traditional running does. ____ ”

    McCarthy thinks that he gets much more exhausted after crunning, so he believes it must burn more calories than running.

     ____ Some believe crunning could result in bad shoulder injuries or broken noses.

    But McCarthy is not worried. Many Melbourne residents have been seen running around on all fours. ____ In the Chinese city of Zhengzhou, crawling, a much slower version of crunning, has been a favourite activity for many years. According to some people there, the exercise is believed to date back two thousand years to the Han Dynasty.

     ____ Then McCarthy advises you to buy some good shoes, hand gloves and most important of all, a face mask!

A. Ready to give crunning a try?

B. As it turns out, they are not the only ones.

C. Crunning seems more difficult than traditional running.

D. It really exercises your legs and shoulders at the same time.

E. It's part of the Internet's latest fitness activities: “Crunning.”

F. However, many are not sure if it is the right exercise for humans.

G. He warns, however, that he can't say whether crunning is potentially harmful.

如图，在平面直角坐标系中，点A在第一象限，AB⊥y轴于点B，函数$y=\frac{k}{x}$（k＞0，x＞0）的图象与线段AB交于点C，且AB=3BC．若△AOB的面积为12，则k的值为（　　）