--> He did not ask me for help
--> Do not have to go to the dentist
--> A Terceira frase deveria ser (They bought their farm).  **Forma negativa: They did not buy his farm

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Tem que estar no presente simples negativo, e não no passado simples negativo
He doesn't ask me for help
we don't go  the dentist´s
they don't buy her fam
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