An alternative way of forming a question is to juxtapose the affirmative and negative forms of the predicative verb or adjective:
她是中國人嗎﹖becomes 她是不是中國人﹖
你忙嗎﹖becomes 你忙不忙﹖
你認識他嗎﹖becomes 你認識不認識他﹖
If the verb or adjective is composed of a single word, then repeat the single word; if two or more words, then repeat them all:
忙不忙, 認識不認識, 介紹不介紹
If the predicative verb takes an object, it is usually only the verb that gets repeated, not the noun following it:
你喝不喝茶﹖
你去不去中國﹖
Sometimes if the object of the verb is not long, one can use the form of "V + object + 不 + V ?" as well, although this is not as common:
你喝茶不喝茶﹖
她去中國不去﹖
As in questions with interrogative words (誰, 什麼, etc), affirmative-negative questions do not take 嗎 at the end.
If an adverb such as 常, 都, 也 or 很 comes /before/ the predicative verb or adjective, do not use the affirmative-negative form but use 嗎 instead:
你們都去中國嗎﹖
but not 你們都去不去中國﹖
他常喝咖啡嗎﹖
but not 他常喝不喝咖啡﹖
Notice, however, that this rule applies only when those adverbs come /before/ the predicative verbs or adjectives. Compare:
她很忙嗎﹖ but not 她很忙不忙﹖
她是很好大夫嗎﹖ 她是不是很好的大夫﹖
The second instance is acceptable because 很 comes /after/ the predicative verb 是.
If there is more than one verb in a sentence, usually only the /first/ verb gets the affirmative-negative form in the question:
你去商店買紙嗎﹖becomes 你去不去商店買紙﹖
他們歡迎我來嗎﹖ becomes 他們歡迎不歡迎我來﹖