The collocations
…才是
…才好 …才行
are placed at the end of a sentence. They set the tone of a sentence, and it is often not translated into English.
Let’s look at each individually.
…才是
…才是 emphasizes that an action has to be done in a certain way.
Scheme
action
才是
Examples
你是哥哥,让着妹妹才是
You are the older brother! You have to give up your seat for your sister
nǐ shì gēge, ràngzhe mèimei cái shì
按天气预报,现在该下雪才是
According to the weather forcast, it should be snowing
àn tiānqì yùbào, xiànzài gāi xià xuě cái shì
…才好
…才好 emphasizes that it is the only right and good way.
This collocation is often used in sentences like "how to do it better", "how to do it right".
Scheme
action
才好
Examples
我就是弄不清做什么才好
I just can’t understand what to do to make it right
wǒ jiùshì nòng bù qīng zuò shénme cái hǎo
这评论让我不知说什么才好
This comment made me wonder how to answer questions better
zhè pínglùn ràng wǒ bù zhī shuō shénme cái hǎo
…才行
…才行 emphasizes that something is only possible in a certain situation.