Hái shì (還是) and huò shì (或是) both could be utilized to present a choice when functioning as conjunctions.
Huò shì (或是) is typically used in declarative sentences, linking all the possibilities together. Therefore, the semantic meaning of huò shì (或是) has the feature [+inclusive].
明年我可能去北京或是上海。
míng nián wǒ kě néng qù běi jīng huò shì shàng hǎi.
Next year I may go to Beijing or Shanghai.
Huò shì (或是) also could be used to provide choices in a question, but the sentence must include a question marker ma (嗎) at the end of the sentence, indicating that it is an interrogative sentence.
明年你想去北京或是上海嗎?
míng nián nǐ xiǎng qù běi jīng huò shì shàng hǎi ma?
Do you want to go to Beijing or Shanghai next year?
Hái shì (還是) is generally used in interrogative sentences and declarative sentences. These sentences contain embedded interrogative clauses. The employment of hái shì (還是) presents a choice between two or more than two options, and the semantic feature of hái shì (還是) is [+exclusive].
明年你想去北京還是上海?
míng nián nǐ xiǎng qù běi jīng hái shì shàng hǎi.
Do you want to go to Beijing or Shanghai next year?
你想喝水，咖啡還是茶？
nǐ xiǎng hē shuǐ, kā fēi hái shì chá?
Would you like water, coffee or tea?
The following sentence is a statement, but it contains a question that remains to be answered. In this case, hái shì (還是) should be used.
我不知道明年應該去北京還是上海。
wǒ bù zhī dào míng nián yīng gāi qù běi jīng hái shì shàng hǎi.
I don't know if I should go to Beijing or Shanghai next year.
