2 sentences

1. 你听说过空气净化器吗？

   nǐ tīng​shuō guo kōng​qì​jìng​huà​qì ma?

   Have you heard of air purifiers?

   Source: CCMatrix

2. 我什么时候应该使用空气净化器？

   wǒ shén​me​shí​hou yīng​gāi shǐ​yòng kōng​qì​jìng​huà​qì?

   When should I use an air purifier?

   Source: CCMatrix