课文：
kèwén

注释：
zhùshì

Exceptions in pronounciation: The modulation of “一” and “不”:

– The modulation of “一” (yī):

“一” (yī) means one, and by itself, it is a first tone syllable. When it is followed by anything, it changes its tone, except for when it is used as an ordinal number. When it is followed by a first, second or third tone syllable, its tone changes from first to fourth tone. If it is followed by a fourth tone syllable, it changes to second tone.

例如(Eg):

When “一” is an ordinal number, the tone remains unchanged.

例如:

第一课 (first lesson)
dì yī kè

– The modulation of “不” (bù):

“不” means “no”, “not”, and the pronounciation should be with the fourth tone, unless followed by another fourth tone syllable. In that case, its tone changes to second tone, so the rule is the same as for “一”.

例如:

不要
búyào

Please note that the above changes are not generally true for all first and fourth tone syllables, they only apply for “一” and “不” in particular.

– “不” (bù) and “没” (méi):

没 (méi) is only used to negate 有 (yŏu), and is often used by itself as an abbreviation for “没有” (méiyŏu). “不” is used to negate verbs other than “有”, and all adjectives.

例如:

不 is also used to negate any adjective.

例如: