He traced that number back to an empty apartment,他追踪那个号码找到了一个空的公寓

track down追捕到，追查出；追寻；查获

She had spent years trying to track down her parents.
她已经花了好多年时间试图追寻父母的下落。

He was determined to track down the cause of food spoilage.
他决心查出食品腐烂的原因.

the landlord said that it was rented out to a girl.房主说以前出租给了一个女孩
rent out租出；出租
She decided to rent out a room to get extra income.
她为获得额外收入决定租出一个房间.
They had to rent out the upstairs to make mortgage payments.
他们不得不将二楼租出去以偿付抵押借款.

He's on his way back from New York right now.他现在正从纽约赶回来
on one's way在路上，在途中

She picked up her bag, and went on her way.

她提起包继续赶路。

On her way back, she dropped by her brother's house.
在回家途中她顺便到弟弟家看看.