I won a prize at the fair last year
It’s the correct answer because “I won” is an action at he completed
The direct object pronoun would be "la" because la gasolina is feminine. In a sentence you could say
La compro en la estacion de servicio.
Direct object pronouns are placed before the verb generally.
La segunda (Es divertida.)
UNA casa GRANDE so "una grande" is the answer
