Mandarin nouns do not have a plural form, but using the adverb dōu implies two or more of an noun.
The adverb dōu translates as all or both. It is used after the noun to be modified:
Wǒmen dōu xǐhuan xīguā.
We all like watermelon. (All of us like watermelon.)
Example of Dōu
Here are some more examples:
Tāmen dōu yào qù Běijīng.
They are all going to Beijing.
Dōngxī dōu hěn piányi.
Everything is cheap.
Shuǐguǒ dōu hěn hǎo chī.
All the fruit is delicious.
Dōu Bù – None Of
The negative of dōu is dōu bù – “none of.” It is used the same way as dōu, placed after the noun it modifies:
Tāmen dōu bù yào qù Běijīng.
None of them are going to Beijing.
Dōngxī dōu bù piányi.
Nothing is cheap.
Shuǐguǒ dōu bù hǎo chī.
None of the fruit is delicious.
When using dōu or dōu bù, the object can be contained in a preceding phrase:
Zhè xie dōngxī, wǒ dōu yào mǎi.
I’m going to buy all of these things. (These things, I’m going to buy all of them.)
(trad) 這些東西, 我都要買｡
(simp) 这些东西, 我都要买｡
The object does not necessarily have to be stated when the context is clear:
Wǒ dōu mǎi le.
I bought all (those things).