What is the coolest gas in the universe? （新增）
What is the coldest air temperature ever recorded on the Earth? Where was this low temperature recorded? The coldest recorded temperature on Earth was -91℃，which occurred（51）in Antarctica in 1983．
We encounter an interesting situation when we discuss temperatures in space（52）.Temperatures in Earth orbit actually range from about 120℃to -120℃．The temperature depends upon whether （53）you are in direct sunlight or shade．Obviously， -120℃is colder than our body can safely （54）endure．Thank NASA science for well-designed space suitsthat protect astronauts from these temperature extremes．
（中间）
In the 1920s，Satyendra Nath Bose was studying an interestingtheory（60）about special light particles we now call photons．Bose had trouble convincing（61）other scientists to believe his theory，sohe contacted Albeg Einstein．Einsteins calculations helped him theorize that atoms would（62）behave as Bose thought--but only at very cold temperatures.
Scientists have also discovered that ultra-coldatoms can help them make the worlds atomic clocks even more（63）accurate．These clocks are so accurate today they would only lose one second every（64）six million years！Such accuracy will help ustravel in space because distance is velocity times time(d=v×t)．With the long distances involved in space travel（65），we need to know time as accurately as possible to get accurate distance．
51．A. opened B. occurred C. opposed D. operated
52．A. Earth B. space C. planet D. star
53．A. whether B. where C. what D. when
54．A. safely B. sadly C. repeatedly D. Freely（换题）
55．A. year B. energy C. system D. rays
56．A. by B. away C. along D. With（换题）
57. A. education B status C knowledge D location
58．A. reasonable B. interesting C. impossible D. necessary
59．A. burnt B. blown C. cut D. cooled（换题）
60．A. invention B. theory C. paper D. experiment
61．A. convincing B. begging C. ordering D. forcing
62．A.would B.will C. must D. need（选项换位）
63．A. that B. such C. much D. more（换题）
64．A. any B. each C. every D. some
65．A. travel B. craft C. age D. station