"The girl eats apples."
Translation:A menina come maçãs.
Seems like that has to do with the verb. In English an example would be "belong to"--the word "belong" never hangs out without the word "to" after it. I think that in Portuguese, the word "comer" does not need a preposition, but the word "gostar" does (to like: "gostar de").
I think this only applies to Portuguese verbs like 'gostar'. 'Gostar de' translates roughly to be 'like of' or 'be pleased by'. The same wouldn't work for other verbs like 'comer'. Gostar means 'taste', but the addition of 'de' makes it mean 'like'.