The reduplication of the interrogative pronouns
Interrogative pronouns can be used in affirmative sentences. In these cases, they are not interrogative.
If these pronouns are used twice in a sentence, the first one is translated as an interrogative pronoun and the second one as a demonstrative pronoun.
For example:
什么…什么… 
Examples
想吃什么就吃什么
Eat whatever you want
xiǎng chī shénme jiù chī shénme
想买什么手机就买什么手机
Buy the phone that you want
xiǎng mǎi shénme shǒujī jiù mǎi shénme shǒujī
Pay attention
The second verb is often preceded by the adverb 就 .
.
These sentences can include two subjects.
Scheme
subject 1
predicate
interrogative pronoun
subject 2
(就)
predicate
interrogative pronoun
Examples
你想买什么手机我就买什么手机
I will buy you the phone you want (Whatever phone you want, I will buy that)
nǐ xiǎng mǎi shénme shǒujī wǒ jiù mǎi shénme shǒujī
什么时候…什么时候…
Examples
你什么时候有空，我什么时候去找你
I will come to you when you have time (When you have time, then I will come to you)
nǐ shénme shíhou yǒu kòng, wǒ shénme shíhou qù zhǎo nǐ
谁…谁…
Examples
谁想参加比赛谁就报名参加
Anyone who wants to take part in the competition can sign up
shéi xiǎng cānjiā bǐsài shéi jiù bàomíng cānjiā
几…几…
Examples
他们几点来就几点开始
They will start as soon as they arrive (The time they arrive is when they start)
tāmen jǐ diǎn lái jiù jǐ diǎn kāishǐ
Pay attention
Note the use of a measure word after 几!
怎么…怎么…
Examples
你怎么做，我就怎么做
I'll do what you do (Whatever you do, that's what I will do)
nǐ zěnme zuò, wǒ jiù zěnme zuò
哪儿…哪儿…
Examples
你愿意去哪儿就去哪儿
Go wherever you want
nĭ yuànyì qù năr jiù qù năr
多少…多少…
Examples
想拿多少拿多少
Take as much as you want
xiăng ná duōshao ná duōshao
哪…哪…
Examples
你想买哪个，就买哪个
Buy whichever you want (Buy whichever one you want to buy)
nǐ xiǎng mǎi nǎ ge, jiù mǎi nǎ ge
Pay attention
Note the use of a measure word after 哪!
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