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我倒能理解以下的說法:
A: 我在家只講客家話.
B: 那 [= 那麼 "then"--used as a cohesive device to link the previous statement with what is going to be said] 客家話你講的是哪一種?
==> 在這例子中, "那" 用來連貫 (to cohere), 而非引介 (to introduce)
And there is a question about '那' in another thread, where contents relating to '那' can be found in #7, #8, the first half of #9 and #10, and #11. Thank you for your reading.
In this example (那,請問能不能給我們一壺茶?), '那' is used to introduce a subject of conversation that is of present interest. That is to say, its main function is subject introduction, especially in form of a question (rather than "cohesion", i.e., connecting with something that has been said).