Generally interchangeable.
高兴 is more general and can be used to describe a wide range of happy or positive emotions, while 开心 is more specifically used to describe a feeling of joy or delight. In general, both words can be used interchangeably to describe happiness, but 开心 tends to be used in more informal or   contexts, while 高兴 is more commonly used in formal or polite settings.
 

Difference between A and B in Chinese with Shanmei

高兴VS开心 differences

the difference between 放松 and 轻松, show me with examples
放松 (fàng sōng) and 轻松 (qīng sōng) are both adjectives that can be translated as "relaxed" in English. However, there are some subtle differences in how they are used.
放松 (fàng sōng)  is a more general term that refers to the state of being relaxed or at ease. For example:
我喜欢做瑜伽，因为它能让我放松。(I like doing yoga because it helps me relax.)
wǒ xǐ huān zuò yú jiā, yīn wéi tā néng ràng wǒ fàng sōng.
假期让我放松许多。(The vacation helped me relax a lot.)
jià qī ràng wǒ fàng sōng xǔ duō.

轻松 (qīng sōng) on the other hand, is often used to describe an activity or task that is easy and not very demanding. For example:
这道题目太轻松了，我很快就会做出来。(This problem is too easy. I'll finish it quickly.)
zhè dào tí mù tài qīng sōng le, wǒ hěn kuài jiù huì zuò chū lái.
这项工作对我来说很轻松。(This job is very easy for me.)
zhè xiàng gōng zuò duì wǒ lái shuō hěn qīng sōng.

So, while both words refer to a state of relaxation, 放松 is more general and refers to a general feeling of relaxation, while 轻松 is more specific and refers to an activity or task that is easy and not very demanding.

Difference between 放松 (fàng sōng) and 轻松 (qīng sōng) 

"不行" (bù xíng) is a more casual and colloquial expression, and it is often used to indicate that something is not feasible or practical. It can be translated as "can't" or "won't work."
"不可以" (bù kě yǐ) is a more formal and polite expression, and it is often used to indicate that something is not allowed according to rules or regulations. It can be translated as "cannot" or "not allowed."
Here are some examples that illustrate the difference between "不行" (bù xíng) and "不可以" (bù kě yǐ):
Example 1:
A: 你能给我五块钱吗？ (nǐ néng gěi wǒ wǔ kuài qián ma?) (Can you give me five dollars?)
B: 不行，我没有五块钱。 (bù xíng, wǒ méi yǒu wǔ kuài qián) (No, I don't have five dollars.)
B: 不可以，这是违反公司规定的。 (bù kě yǐ, zhè shì wéi fǎn gōng sī guī dìng de) (No, it is against company rules.)
In the first example, "不行" (bù xíng) is used to indicate that the person does not have the requested amount of money. In the second example, "不可以" (bù kě yǐ) is used to indicate that giving the money is against company rules.
"不行" (bù xíng) might be more appropriate if the person simply does not have the requested amount of money, while "不可以" (bù kě yǐ) might be more appropriate if there is a rule or regulation that prevents the person from giving the money.

Example 2:
A: 你能把这个盒子放在桌子上吗？ (nǐ néng bǎ zhè gè hé zǐ fàng zài zhuō zi shàng ma?) (Can you put this box on the table?)
B: 不行，它太大了。 (bù xíng, tā tài dà le) (No, it is too big.)
B: 不可以，桌子上没有足够的空间。 (bù kě yǐ, zhuō zi shàng méi yǒu zú gòu de kōng jiān) (No, there is not enough space on the table.)
In the first example, "不行" (bù xíng) is used to indicate that the box is too large to fit on the table. In the second example, "不可以" (bù kě yǐ) is used to indicate that there is not enough space on the table.
"不行" (bù xíng) might be more appropriate if the box is too large to fit on the table, while "不可以" (bù kě yǐ) might be more appropriate if there is not enough space on the table.



Difference between "不行" (bù xíng) and "不可以" (bù kě yǐ)

不免 (bù miǎn) and 未免 (wèi miǎn) are both adverbs that are used to indicate that something is inevitable or cannot be avoided. However, there is a subtle difference in their meanings.
不免 (bù miǎn) means "inevitably" or "unavoidably," and it is used to indicate that something is certain to happen or cannot be avoided. Here is the structure when using 不免：objective reason,+不免+result
未免 (wèi miǎn) means "unavoidably" or "unnecessarily," and it is used to indicate that something is unnecessary or excessive. You use it when you can’t agree to something. Here is the structure when using 未免：（scenario, can be omitted in the sentence)，+未免+judgement
Here are some examples to illustrate the difference between the two, with pinyin provided for the example sentences:
不免 (bù miǎn)
* 这种天气下出门，不免有些冷。 (zhè zhǒng tiānqì xià chūmén, bù miǎn yǒuxiē lěng) (It is inevitably a little cold when going out in this kind of weather.)
* 他的职业生涯结束了，不免有些伤感。 (tā de zhíyè shēngyá jiéshù le, bù miǎn yǒuxiē shāngǎn) (His career has ended, and it is inevitably a little sad.)
未免 (wèi miǎn)
* 这道题的难度未免有点大。 (zhè dào tí de nándù wèi miǎn yǒudiǎn dà) (The difficulty of this problem is unnecessarily large.)
* 他的表演未免有些夸张。 (tā de biǎoyǎn wèi miǎn yǒuxiē kuāzhāng) (His performance is unnecessarily exaggerated.)
* 你这么做，未免太过分。 (nǐ zhème zuò, wèi miǎn tài guòfèn) (What you are doing is unnecessarily extreme.)
