阅读下列短文，从每题所给的四个选项(A、B、C、D)中，选出最佳选项。

　　Astronauts on shorter shuttle missions(使命)often work very long days．Tasks are scheduled so tightly that break times are often used to finish the day's work．This type of schedute is far too demanding for long missions on the Internaitional Space Sttation(ISS)．ISS crewmembers usually live in space for at least a quarter of a year．They work five days on and two days off to mimic the normal way they do things on Earth as much as possible．Weekends give the crew valuable．Weekends give the crew valuable time to rest and do a few hours of housework．They can communicate with family and friends by email, isternet phone and throhgh

　　Private video conferenes．

　　While astronauts cannot go to a baseball game or a movie in orbit, there are many familiar activetics that they can stil enjoy．Before a mission．The family and friends of each ISS crewmember put together a collection of family photos, messages, videos and reading material for

　　The astromauts to look at when they will be floating 370 kilometers above the Earth．During ther missiom, the crew also receives care packages with CDs, books, magazines, photos and letters．And as from early 2010, the internet became available on the ISS, giving astronaouts the chance to do some “web surfing(冲浪)” in their personal time．Besides relaxing with these more commom entertainments, astromauts can simply enjoy the experience of living in spaec．

　　Many astronauts say that one of the most relaxing things to do in spaec is to look out the window and stare at the universe and the Earth's vast land mass and oceans．

(1)

(2)

(3)

(4)