дверей

дверей

"Дверей" means "of doors" (genitive plural form).

Here, 'дверей' is used as the genitive plural form of 'дверь' indicating 'of the doors', following the word 'одну из' which implies selection from a group.

Она открыла одну из дверей и вошла.

She opened one of the doors and entered.

In this sentence, 'дверей' is in the genitive plural case, showing possession with 'на' indicating placement 'on the doors'.

Замок на дверей был старым, но все еще рабочим.

The lock on the doors was old but still functional.

Here, 'дверей' is used in the genitive plural form because it follows 'множество', describing 'of doors' in the context of 'many doors'.

Мы видели структуру со множеством дверей.

We saw a structure with many doors.