Okay. My translation was 'The mirror continues here' by which I imagined that a mirror (say a stripe of mirror) on a wall continues here (on this adjacent wall or door or whatever). It was accepted by the system, however, it is a completely different meaning. Can the original portuguese sentence mean also this, or only the meaning you have discussed: 'remains' 'still is' etc?
be careful with the english. In the infinitive, "to be still somewhere" means "to be somewhere, while holding still / not moving" (like an animal hiding in a hiding spot). To still be somewhere / to be somewhere, still" is the meaning you want. In contrast, "i am still somewhere" or "he is still somewhere" means what you want it to mean.
It's an awkward situation caused by "being still" meaning "to be in a position of suspended movement" (something that normally moves, being intentionally, temporarily motionless). Similarly, the imperative, "be still," means, "stop moving!"
"Keeps" is a transitive verb that requires an object.* You could, for example, say that a person keeps a mirror on his desk.
*With one exception: When referring to something perishable, you can use "keeps" to indicate that the perishable item does not go bad. Examples: Vegetables usually keep better in the fridge. Milk still keeps for several days after its sell-by date.