第6部分：完形填空（第51～65题，每题1分，共15分）
下面的短文有15处空白，请根据短文内容为每处空白确定1个最佳选项。
What Is the Coolest Gas in the Universe？
What is the coldest air temperature ever recorded on Earth？Where was this low temperature recorded？The coldest recorded temperature on Earth was-90℃，which 51 in Antarctica（南极洲）in 1983.
We encounter an interesting situation when we discuss temperatures in 52 .Temperatures in Earth orbit（轨道）actually range from about+120℃to-120℃.The temperature depends upon 53 you are in direct sunlight or in shade.Obviously，-120℃is colder than our body can 54 endure.
The space temperatures just discussed affect only our area of the solar 55 . Obviously，it is hotter when closer to the Sun and colder as we travel 56 from the Sun. Scientists estimate temperatures at Pluto are about-210℃.How cold is the lowest estimated temperature in the entire universe？Again，it depends upon your 57 .We are taught it is supposedly 58 to have a temperature below absolute zero，which is-273℃，at which atoms do not move.Two scientists，Cornell and Wieman，have successfully 59 down a gas to a temperature barely above absolute zero.They won a Nobel Prize in Physics in 2001 for their work—not a discovery，in this case.
Why is the two scientists’work so important to science？
In the 1920s，Satyendra Nath Bose was studying an interesting 60 about special light particles（微粒）we now call photons（光子）.Bose had trouble 61 other scientists to believe his theory，so he contacted Albert Einstein.Einstein’s calculations helped him theorize that atoms 62 behave as Bose thought—but only at very cold temperatures.
Scientists have also discovered that ultra-cold（超冷）atoms can help them make the world’s atomic clocks even 63 accurate.These clocks are so accurate today they would only lose one second 64 six million years！Such accuracy will help us travel in space because distance is velocity（速度）times time（d=υt）.With the long distances involved in space 65 ，we need to know time as accurately as possible to get accurate distance.
51.A.operated B.occurred C.opened D.offered
52.A.star B.Earth C.space D.planet
53.A.whether B.where C.what D.when
54.A.safely B.sadly C.repeatedly D.freely
55.A.system B.energy C.year D.rays
56.A.by B.away C.along D.with
57.A.education B.status C.knowledge D.location
58.A.impossible B.interesting C.reasonable D.necessary
59.A.burnt B.blown C.cut D.cooled
60.A.invention B.experiment C.theory D.paper
61.A.forcing B.begging C.ordering D.convincing
62.A.would B.will C.must D.need
63.A.that B.such C.much D.more
64.A.any B.each C.some D.every
65.A.station B.craft C.travel D.age