多年前，内蒙古乌拉特前旗杨树林场的光肩星天牛泛滥，科学家为此引进了几百只以天牛幼虫为食的大斑啄木鸟．现在，林场中很少再见到光肩星天牛了．这种现象叫做（  ）

某颗行星的同步卫星正下方的行星表面上有一观察者，他用天文望远镜观察被太阳光照射的此卫星，发现日落的 $\frac{T}{2}$ 时间内有 $\frac{T}{6}$ 的时间看不见此卫星．（已知该行星自转周期为T，该行星半径为R不考虑大气对光的折射，）则该同步卫星距该星球的高度是（   ）

①有助于更好了解人类文化的多样性    ②有利于推动中华文化更好地走向世界

③有利于促进中英两国文化的交流      ④商业贸易是文化交流的重要途径

根据短文内容，完成下列各题。

    In China, September 10th is a special day. It's Teachers' Day. Teachers' Day began in 1985. It is a great day for all the teachers and also a happy time for us students. How do we spend Teachers’ Day every year?

    On that day, we go to school early in the morning, and put a bunch (束) of flowers on our teacher's desk to give him or her a big surprise. Some of us help him or her to do some easy work. And others stand at the school gate to say hello to teachers when they go into the school.

    In the afternoon, we have a party. We sing and dance with the teachers.

    All of us are very happy. The teachers say that the best reward (奖励，奖赏) for them is to see our great progress(进步).