The translation su agrees in number with the noun which it modifies; their is translated by su, sus, depending on what follows: their father/mother su padre/madre; their books/magazines sus libros/revistas. For their used with parts of the body,
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The National Police (Policía Nacional) was set up in Spain in 1976. Its members patrol provincial capitals and big cities, which are responsible for its finance, administration, and recruitment. Although armed, it has never been considered a repressive force, unlike the