There are four seasons in a year. They are spring, summer, autumn and winter. For all my friends, every season is good.

    Wang Dong likes flying kites and climbing hills. She says when spring comes, the days are getting warmer and longer. And everything begins to grow. The wind is not very strong. It's the best time to fly kites. And when you climb the hills, you can enjoy yourself. So she often says spring is her favourite season.

    "Swimming is my favourite sport,”says Anne. “When summer comes, I often go swimming in the rivers or lakes with my friends." You can enjoy yourself in the water.And you can swim like a fish there.

    “I often go climbing hills with my father during the long vacation of the National Day, ”says Liu An. “My father often tells me that I can see lots of beautiful things if I stand on the top of a hill. ”So he likes autumn best of all.

    Bob says he likes winter very much. He says, “I'm very happy when I am playing with snow.”He is making a snowman now.

已知递减的等差数列{a_n}满足${a_1}^2={a_9}^2$，则a₅=（　　）

谭维维的歌曲《华阴老腔一声喊》喊出了对美好生活的热切渴望：“……不怕汗珠摔八瓣，……咱脸朝黄土背朝天，希望种进那黄土地，只盼着结出金蛋蛋”，要想让“黄土地”结出“金蛋蛋”，实现中华民族复习的中国梦，我们应该（　　）

①发扬艰苦奋斗精神                                        ②弘扬爱国主义为核心的民族精神和以改革创新为核心的时代精神

③我国要实施科教兴国和人才强国战略        ④全面贯彻“创新、协调、绿色、开放、共享”的五大发展理念

作家余秋雨曾写道：就在秦始皇下令修长城的数十年前，四川的成都平原上已经完成一个了不起的工程……而它至今还在造福民众。这个了不起的工程是（　　）