What's the red star in the sky through a telescope(望远镜)? It is Mars. Do you want to know more about it? Take the “Mars Orbit Express”!
  “Mars Orbit Express” is a space probe (探测器). It was sent towards Mars by American scientists on August 12th, 2005. Its tasks are to study Mars' atmosphere and return photos to Earth. But before that “Mars Orbit Express” must travel about 100 hundred million kilometers and seven months. It reached Mars' orbit(轨道)in March, 2006.
    Mars and Earth have similar weight and size. However, Mars is closer to the sun than Earth. Mars is very cold. The average temperature is below 50℃. The temperature at noon only reaches 20℃ during a Mars day. Its atmosphere is mostly CO2. It has much sand and two moons---Phobos and Deimos.
    Scientists think Earth and Mars had similar beginnings 4.6 billion years ago. But while Earth supports millions of lives，Mars becomes bad. “Earth easily could have turned out like that.” said an scientist, “It is important for us to find out why and Mars Orbit Express' should do that.” “Mars Orbit Express” also would help scientists to learn what might happen to Earth in the future.  “Mars Orbit Express” would work for about four years.

如图，在地面上离旗杆BC底部18米的A处，用测角仪测得旗杆顶端C的仰角为30°，已知测角仪AD的高度为1.5米，那么旗杆BC的高度为____米．

    I have a friend. His name is Jack. ③He is healthy because(因为) he plays sports. He runs every day. He runs to his ___①____ in the morning and he runs ____②____ after school in the afternoon. He can run fast. He likes playing soccer, volleyball, tennis, basketball , ping-pong and more. He has three soccer balls, two volleyballs, six tennis rackets, four basketballs and many ping-pong balls. They are in his room. He plays sports with his friends every day. He likes many sports stars and he often watches them on TV. All my classmates say Jack is sporty (爱好体育)。

运输里程是交通网中某种运输方式线路总长度，下图是1979-2014年我国各种运输方式里程变化统计图，公路里程比是指公路实际长度与起迄点间线段长度的比值。华北地区平原国道的里程比高于东北平原，主要是因为华北平原（    ）