inseparable

Since they met in primary school, the two best friends have been inseparable.

(Chinese) 自从在小学相识以来，这两个最好的朋友就一直形影不离。

In many modern cities, cars and traffic jams have become inseparable problems.

(Chinese) 在许多现代城市中，汽车与交通拥堵已成为密不可分的问题。