Long vowels are clearly distinct from short vowels since every shortvowel, every single one, has a doubled consonant after it.
长元音与短元音泾渭分明,因为每一个短元音后都双写了辅音。
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The word "look" is sometimes classified as a "shortvowel" because the "oo" sounds different in words like "spook". However, the word "looking" needs a stronger emphasis and an extension of the vowel.