辛亥革命之后，中国“名为共和国，实际上仍旧由军阀掌握政权”。观察右图，你认为占据图中所示区域的军阀是(    )

东北兴安岭山地是我国重要的林区，新修筑的铁路进入林区后，林区人民高兴的说：“火车一响，黄金万两”这说明（    ）

    People from all over the world make friends____ writing letters. One way to find a pen friend is to ____ a club. International Pen Friends started in 1967 and has over 300,000members(成员) in different countries. Their____ member is eight years old, and their oldest member is over 80. Some people write to find out about life in another country, ____ want to practice their English, or enjoy their hobbies. Stamp collectors, for example, write to people in different countries ____ that they can collect the stamps on the letters they receive. Most people just enjoy making friends, and they invite their pen friends to visit them.

在“分离土壤中分解尿素的细菌”实验中，为判断是否起到了分离效果，提高实验结果的可信度，需要精心设置对照．对照组的设置方式为（ ）