Wǒ fù xiānjìn.

我付现金。

I'll pay by cash.

Notes:

(wǒ): I

(): to pay

现金(xiānjìn): cash

Example:

A:你付现金吗?

     Nǐ fù xiānjìn mɑ?

     Will you pay by cash?

B:我付现金。

     Wǒ fù xiānjìn.

     I'll pay by cash.

Level: