Дупло
сущ., ср.рода, им.падеж, ед.число : (there lives a squirrel).
Then:
Две белки выглянули из своих [...]
(there will be a pl.noun in this field)
(a couple ways to answer ...)
- Дупл
- Дупел
- Дуплей
- ???
The question is: why have Russians faced difficulties in constructing such example?