Final answer:
According to sources, smartphones likely comprised the majority of Pandora users' listening equipment in 2017.
Step-by-step explanation:
According to the sources cited, 35% of American adults owned smartphones in 2011 (Smith, 2011) and there are statistics on smartphone users by the numbers (Visually, 2013). Therefore, it is likely that smartphones comprised the majority of listening equipment for Pandora users in 2017. Smartphones are portable electronic devices connected to speakers, making them convenient for listening to music. Car radios and home stereos are limited in terms of portability, and desktop computers are less commonly used for listening to music compared to smartphones.