The landlord had let the building fall into decay.

房东不管，房子已经破烂不堪。

Old civilization may fall into decay.

古老的文化可能会渐渐衰落下去。

The old civilization may fall into decay.

古代的文化可能衰落。

The old civilization may fall into decay .

古代的文化可能衰落。

The buildings had started to fall into decay.

这些建筑物开始衰败。