同学们在历史研究性学习中，搜集了以下图片。从这些图片可以看出他们研究的主题是（    ）

该图为我国某城市发展过程中1990年和2010年比较图。

   Some people don’t like doing sports because they think it is hard work and will make____ (他们) feel tired . That’s wrong! Sports help us to____ (保持)healthy , happy and live longer .If you____ (从不) do sports , you will get unhealthy easily . Sports are____ (也)a good way to make friends .People from different____ (地方) may not know each other , but after a game , they often become good friends .And sports in winter and ____ (夏天)are not the same.____ __(swim) is fun in hot weather , while skiing is great____ cold days . Many people____ (享受) watching others play games .They often get very____ (兴奋) when “their” players or teams win .