Usage of "不（bù）". (1) To express one's willingness or unwillingness. For example, 他不想去上课（tā bú xiǎng qù shàng kè）He doesn't want to go to class. (2) To deny a regular or habitual situation. For example, 他不喝酒（tā bú hē jiǔ）He doesn't drink. (3) Fixed collocation "不会、不是、不知道、不应该、不……（bú huì 、bú shì 、bú zhī dào 、bú yīng gāi 、bú ……）" expresses judgment, estimation or perception. For example, 你不应该去找他（nǐ bú yīng gāi qù zhǎo tā）。You shouldn't go to him. 我不是她的汉语老师（wǒ bú shì tā de hàn yǔ lǎo shī）。I am not her Chinese teacher. (4) Negate having a certain nature or state. For example: 这些苹果不红（zhè xiē píng guǒ bú hóng）。These apples are not red. Usage of "没（méi）". (1) An objective narrative that denies that an act has occurred. For example, 昨天他没去，因为他很忙（zuó tiān tā méi qù ，yīn wéi tā hěn máng ）。he didn't go yesterday because he was busy. (2) To deny that something has happened. For example, 他刚才没吸烟（tā gāng cái méi xī yān ）。he didn't smoke just now. (3) Negation of "有（yǒu ）" . For example: 我有哥哥，没有弟弟（wǒ yǒu gē gē ，méi yǒu dì dì ）。I have older brother, no yonger brother. (4) To deny that the nature or state has changed. For example: 这些苹果没红（zhè xiē píng guǒ méi hóng ）These apples are not red. Look at the difference between "不" and "没" in the following examples! 1. 他不想去上课（tā bú xiǎng qù shàng kè）He doesn't want to go to class. (To express one's willingness or unwillingness, to deny subjectivity) 昨天他没去，因为他很忙（zuó tiān tā méi qù ，yīn wéi tā hěn máng ）He didn't go yesterday because he was busy. (Objective account) 2. 他从来不喝酒也不吸烟（tā cóng lái bú hē jiǔ yě bú xī yān ）。He never drinks or smokes. (Negate regular or habitual situations) 他刚才没吸烟（tā cóng lái bú hē jiǔ yě bú xī yān ）。He didn't smoke just now. (Negate that an act has taken place) 3. 这些苹果不红（zhè xiē píng guǒ bú hóng）。These apples are not red. (Deny having a certain nature, state) 这些苹果没红（zhè xiē píng guǒ méi hóng ）。These apples are not red. (Negate that the nature, state has changed)

二 (èr)" VS. "两 (liǎng) The words "二 (èr)" and "两 (liǎng)" have the same meaning, but there is a difference in usage. 1. The ordinal number can only use "èr", not "liǎng", such as "èr nián jí (second year)" and "(èr yuè fèn) February". 2. The base number can use "èr", but also "liǎng". Such as "(èr shí) twenty", "(liǎng qiān) two thousand", etc. But not in any case can be replaced, in the general quantifier before the use of "liǎng" rather than "èr". For example, "(liǎng běn shū ) two books" and "(liǎng gè rén) two people", not "èr běn shū" and "èr gè rén". 3. The quantifiers for weights and measures can be preceded by “liǎng” or “èr”. For example, "(liǎng chǐ bù) two feet of cloth" can also be said as "(èr chǐ bù ) two feet of cloth". 4. When two and three are used in a row, the number does not exceed ten, and generally "liǎng" is used instead of "èr". For example, "(liǎng sān gè ) two or three" is not said as "èr sān gè", and when the number exceeds twenty, "èr" is generally used instead of "liǎng". For example, "(èr sān shí wàn) two or three hundred thousand". "liǎng" is only used for counting words, such as "liǎng gè"两个, "liǎng tiān" 两天. "èr" is often used in ordinal words, such as "dì èr " second.

吧 (ba) 1. used at the end of an imperative sentence to make the tone more soothing: 咱们走吧 (zán men zǒu ba ). 2. used at the end of a declarative sentence to make the tone less certain: 你明天能见到他吧（nǐ míng tiān néng jiàn dào tā ba ） 3. used at the end of a question to make the original question with a speculative, estimated meaning: 这座楼是新的吧？ （zhè zuò lóu shì xīn de ba?） 4. in the sentence to indicate a pause, with a hypothetical tone (often held up, with the implication of a dilemma): 走吧，不好；不走吧，也不好。（zǒu ba ，bù hǎo ；bù zǒu ba ，yě bù hǎo。 ）