Danny is a schoolboy. He 1 in a small town. His home is about ten miles  2 school and the roads are not flat(平坦的). So it's 3 for him to get to school. He 4 at about five thirty every day and has breakfast. Then he5 school at around six o'clock. First, he6 his bicycle to the bus station. That takes about forty minutes.7 the bus takes him to school. It usually takes about thirty minutes. Sometimes he has8time for breakfast at home, so he has something for breakfast on the bus.
   “I've never taken trains. It must be a lot9fun than taking buses,” says Danny. He studies very10at school. He hopes he can go to school in a big city some day. He can take a train to school then.

材料一：冷凉蔬菜是指在气候冷凉地区夏季生产的蔬茉，其最适宜生长温度在17℃-25℃范围，冷凉蔬菜“家族”里有菜花、甘蓝，姓娃菜、西兰花、洋葱、青笋等，冷凉蔬菜在宁夏、甘肃，青海又叫作高原夏菜，在内蒙古，河北称为错季蔬菜，而在云贵川则称为反季节蔬菜，其共同特点是气候冷凉，位于高山，高原或毗邻大草原，大森林，与传统老农耕区及老工业区具有天然的隔离条件，产品具有天然环保无污染的优势。

材料二：兰州市输中县所辖区域海拔多在1500-3300米之间，生长着200多个品种的高原夏菜，菜农多采用山泉水灌既，农家肥使用较多，极少有病虫害，每年5月-10月，当高温笼罩上海、广州等城市时，兰州高原夏菜由一辆辆大货车源源不断地运向南方市场，给暑热的南方带去绿色蔬菜的清香，

材料三：榆中县是兰州市冷凉蔬菜的主产区、随着蔬菜产量的增加，大量尾菜堆积成为一大“公害”，给蔬菜生产基地环境安全造成了威胁，下图所示为兰州市榆中县某示范区的尾莱综合利用示意图。

被减数减少2.4，减数增加2.4，差不变。（   ）

下列属于生态系统的是（  ）