Preterite-Ser and Ir

How do we know that we are using the preterite form of ir in the following sentence?  
José fue a comprar jabón en la farmacia.  

• we are using ir + a + infinitive
• we are describing a person or a thing
• the conjugation is follow by the spanish form of "to the"
• we are saying where someone was at.

How do we know that we are using the preterite form of ir in the following sentence?  
Mariana y sus amigas fueron al cine para ver una pelicula.

• the conjugation is followed by a noun
• the conjugation is followed by the Spanish form of "to the"
• the conjugation is followed by a participle
• the formula ir +a+infinitive is found in the sentence

What infinitive are we using in the preterite tense?
Ayer(yesterday) Elena fue la directora del club escolar.  

• ir
• estar
• tener
• ser

What infinitive are we using in the preterite tense?
Los chicos fueron a comprar raquetas de tenis anoche.

• ser
• ir
• estar
• tener

What infinitive are we using in the preterite tense?
Mi abuela fue al supermercado para comprar frutas.

• ir
• estar
• ser
• hacer