I'm not certain who was there.

　　我無(wú)法確定誰(shuí)當時(shí)在場(chǎng)。

　　You know who I'm referring to.

　　你知道我指的是誰(shuí)。

　　Who cooked this? It's delicious.

　　誰(shuí)做的？味道好極了。