¿cuál es el mejor complemento para la siguiente oración? el tren viajaba cuando de repente llegó a la parada llegaba a la parada llega a la parada

El tren viajaba cuando de repente llegó a la parada.

Explanation:

El tren viajaba cuando de repente llegó a la parada. This means: the train was traveling when suddenly it arrived to the stop. The sentences combines the imperfect with the preterite. This is because an action was taking place in the past, in this case "el tren viajaba" when some other action interrupted it, in this case "llegó". This is the typical combination of those tenses. The imperfect is used for the action that gets interrupted by the precise action in the preterite.

corras is the only one that is informal but doesn't follow the suffix rule. correr is the verb. corre is the formal verb form. corra would be used as the formal is corre ended with an a.

your best bet would be corras, it's the only one that is informal but is still wrong