Negative adverb “不 (bù) no/not” can be placed in front of a verb or adjective to make its meaning negative. “不 (bù) no/not” has the 4th tone, but when it is followed by another 4th tone, it becomes 2nd tone. An example of the change in tone is “不是 (bù shì) is not” is pronounced “bú shì.”
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