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Why is the two scientists work so important to science? In the 1920s,Satyendra Nath Bose was studying an interesting ____about special light particleswe now call photons.Bose had trouble ____ other scientists to believe his theory，so he contacted Albert Einstein.Einsteins calculations helped him theorize that atoms ____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 ____accurate.These clocks are so accurate today they would only lose one second ____six million years! Such accuracy will help us travel in space because distance is velocity times time.With the long distances involved in space ____，we need to know time as accurately as possible to get accurate distance. 51.A. operated B. opened C. offered D. occurred 52.A. space B. star C. Earth D. planet 53.A. where B. what C. when D. whether 54.A. sadly B. repeatedly C. Freely D. safely 55.A. energy B. year C. system D. rays 56.A. by B. along C. away D. With 57.A. location B education C status D knowledge 58.A. interesting B. impossible C. reasonable D. necessary 59.A. burnt B. cooled C. blown D. cut 60.A. invention B. experiment C. paper D. theory | 
