你nǐ知zhī道dào这zhè是shì谁shuí写xiě的de吗ma？

Do you know who wrote this?

门mén口kǒu有yǒu人rén，不bù知zhī道dào是shì谁shuí。

There is someone at the door; I do not know who it is.

你nǐ在zài等děng谁shuí？他tā还hái没méi来lái吗ma？

Who are you waiting for? Has he not arrived yet?

谁shuí在zài敲qiāo门mén？

Who is knocking at the door?

谁shuí愿yuàn意yì帮bāng我wǒ？

Who is willing to help me?