The strategy that allows us to focus only on those stimuli we want to be focused on is known as selective attention, and this is achieved because our brains can put on their efforts to filter the information arriving at it, for example, the things we see with the light rays passing through our eyes, or the sounds we hear reaching our ears in form of sound waves.
The correct answer then is the first one: With thousands of stimuli around us all the time, we choose to focus on a few because we gave those stimuli selective attention.