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there are some new pupils in our group
there is no book on the table
there is an apple on the table
there are 7 days in a week
there is a book in the shelf

There were some new pupils in our group. There will be some new pupils in our group.

There was no book on the table. There will be no book on the table.

There was an apple on the table. There will be an apple on the table.

There were 7 days in a week. There will be 7 days in a week.

There was a book on the shelf. There will be a book on the shelf.