Ответ:
There is a desk but there isn't a dining table.
There are some bookshelves but there aren't any cupboards.
There is a chair but there isn't a armchair.
There are some pictures but there aren't any posters.
There is a rug but there isn't a carpet.
There are some books but there aren't any magazines.
There is a TV but there isn't a computer.
There are some vases but there aren't any mirrors.
Объяснение:
Если у нас предмет в ед. числе, то используем конструкцию (there is a - a неопредеоенный артикль ставится перед предметами в ед. числе, которые можно посчитать. a = one)
Если у нас мн. число (окончание s), то используем вторую конструкцию (there are), а так как у нас предметы во множественном числе не посчитаны, то используем some (несколько) и any (какой-нибудь).