theirs

Our car is the silver sedan, but the blue SUV parked next to it is theirs.

(Chinese) 我们的车是那辆银色轿车，停在旁边的蓝色SUV是他们的。

The decision to move forward with the project was entirely theirs to make.

(Chinese) 推进该项目的决定完全由他们自己做出。