For this case, what we should do is fill in the blank with the correct word.
We observe that we have a sentence where we should look for an alternative to go up to a place.
The two possible options are:
1) Stairs
2) Elevator
As the stairs already appear in the sentence, then we must fill in the blank space with the second alternative.
Completing the sentence in Spanish we have:
Yo uso la escalera o el ascensor para subir a mi habitación.
The translation of the sentence in English is:
I use the stairs or the elevator to go up to my room.
Answer:
"ascensor"
Yo uso la escalera o el ascensor para subir a mi habitación.