In the text below some words are missing. Drag words from the box below to the appropriate place in the text. To undo an answer choice, drag the word back to the box below the text.
下面的文本缺了一些词。请把词框里的词拖到文中合适的位置；要撤销选择，把词拖回文本下方的词框即可。
The speed of sound (otherwise known as Mach 1) varies with temperature. At sea level on a “standard day,” the temperature is 59°F, and Mach 1 is approximately 761 mph. As the altitude increases, the temperature and speed of sound decrease until about 36,000 feet, after which the temperature steady until about 60,000 feet. Within that 36,000–60,000 foot range, Mach 1 is about 661 mph. Because of the , it is possible for an airplane flying supersonic at high altitude to be slower than a subsonic flight at sea level. The transonic band (the “sound barrier”) extends around Mach .8—when the first supersonic shock waves the wing—to Mach 1.2, when the entire wing has gone supersonic.
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