4 sentences

1. 十二月有三十一天。

   Shí'èr​yuè yǒu sān​shí​yī tiān.

   December has thirty-one days.

   Source: Tatoeba

2. 十二月是这一年的最后一个月。

   Shí'èr​yuè shì zhè yī nián de zuì​hòu yī​gè yuè.

   December is the last month of the year.

   Source: Dong Chinese Dictionary

3. 每年的十二月一日是世界抗艾日。

   měi nián de Shí'èr​yuè yī​rì shì shì​jiè kàng ài rì.

   December 1st every year is World AIDS Day.

   Source: Dong Chinese Dictionary

4. 每到农历十二月，家里就开始忙着准备年货。

   měi dào nóng​lì Shí'èr​yuè, jiā​lǐ jiù kāi​shǐ máng zhe zhǔn​bèi nián​huò.

   Every year in the twelfth month of the lunar calendar, the family starts getting busy preparing for the Lunar New Year.

   Source: Dong Chinese Dictionary