Who's that book by?

谁是那本书的作者？

《牛津词典》

"Who's that with you?"—"A friend of mine."

“和你在一起的那个人是谁？”—“我的一位朋友。”

《柯林斯英汉双解大词典》

Who's that boy? Who's that girl?

那男孩是谁？那女孩是谁？

youdao

"Let me get back to you on that. Oh,oh,oh -- in college, the boyfriend who absolutely forgot Valentine's Day.

VOA: special.2010.02.08

That's terrible. Who's that guy that does those commercials?

当时为他做宣传的人是谁

耶鲁公开课 - 美国内战与重建课程节选

And so to see somebody so prolific and who's been that way since he was a teenager, I mean,

所以，（我们）看到这样一个从青年时期就多产的作家，我的意思是，

和男朋友在一起 - SpeakingMax英语口语达人

Come January, we look in the mirror and ask ourselves: Who's that flabby person staring back at me?

CNN: Site Seer: Get fit on the Net

That's who we are. (Applause.) That's who we are and that's what's at stake in this election.

WHITEHOUSE: Remarks by the President at a Campaign Event -- Boulder, CO

Who's that young guy who's going to come up?

WSJ: New York Yankees: Searching for Life Amid the Fossils