a su primer testigo

their first witness

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phrase Rare #49,700
their first witness The personal a before a person as the object of llamar is not translated into English. Su can mean his, her, its, or your (formal), depending on context.
SP: El juez llama a su primer testigo.
EN: The judge calls their first witness.

¿Listos para llamar a su primer testigo?

Ready to call your first witness?

— Cuestión De Honor (1992)

La corona llama a su primer testigo.

The crown calls its first witness.

Por favor, llame a su primer testigo.

Please call your first witness.

Llame a su primer testigo.

Call your first witness.

La corona puede llamar a su primer testigo.

The crown may call its first witness.