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麻醉药品专用处方应由药剂科留存( )年备查
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A Canadian researcher has discovered that sound travels (21) air more than one-half kilometer an hour slower than had been believed. The discovery has surprised many engineers and scientists who learned they had been (22) the wrong speed of sound for many years.The speed of sound in air had been (23) to be three-hundred-thirty-one-point-two-nine meters a second. But Doctor George Wong found, (24) accident, that the speed of sound is only three-hundred-thirty-one-point-one-three meters a second. That is a difference of about sixteen centimeters a second.Doctor Wong is a member of the National Research Council of Canada. He was studying ways to (25) exactly the sound created by microphones. One of his experiments (26) a number he could use to find the speed of sound. He was (27) to learn that the speed of sound was slower than scientists had thought.To explain the difference, Doctor Wong spent eighteen months (28) past test research on the speed of sound. He finally found the (29) of the difference. It was a mathematics mistake (30) in Nineteen-Forty-Two by physicist H-C Hardy.Doctor Wong’s (31) does not mean a big change for the science of sound. This is (32) Doctor Hardy and Doctor Wong measured the speed of sound for what is called" standard air".Standard air exists only (33) thought. It is a way for scientists to agree (34) the same speed of sound. (35) the air around us, standard air always has a temperature of zero degrees Celsius and the same atmospheric pressure (36) the air at sea level. Standard air always has same amounts of nitrogen, oxygen, carbon dioxide and (37) gases. And in standard air, the speed of sound does not change.The change in the new speed of sound is (38) small to affect the work of most sound scientists and engineers. But scientists say Doctor Wong’s discovery may (39) improve instruments (40) use the speed of sound to measure very short distances. 23().
Visual FoxPro支持两种类型的菜单，分别为______。
根据《公司法》的规定，下列人员中，可以担任公司监事的是( )。
下列命令结果中，肯定生成一个空表的是______。
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