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Ando meio destreinado no inglês, mas acredito que você deva passar as pessoas do singular para o plural e tirar os "a" e "an" que significam "um".

Salvo engano meu, devem ficar assim:

We were happy boys

You were godd workers ( o "you were" é igual tanto no singular como no plural)

They were olg formers

They were beautiful girls

We are happy boys.

You were good workers.

They are old farmers.

They are beautiful girls.