[单选题]液化气回收系统正常运转时，脱丁烷塔回流罐干气在压力控制下排至(　　)。
A.燃料气系统
B.火炬
C.液化气罐
D.作为干氢送界外

{{B}}The Mir Space Station{{/B}}
The Russian ’Mir Space Station, which came down in 2001 at last after 15 years of pioneering the concept of long-term human space flight, is remembered for its accomplishments in the human space flight history. It can be credited with many firsts in space.
During Mir’s lifetime, Russia spent about USS 4.2 billion to build and maintain the station.
The Soviet Union launched Mir, which was designed to last from three to five years, on February 20, 1986, and housed 104 astronauts over 12 years and seven months, most of whorh were not Russian. In fact, it became the first international space station by playing host to 62 people from 11 countries. From 1995 through 1998, seven astronauts from the United States took turns living on Mir for up to six months