Respuesta :
el río should be your answer. río is river.
pepa estaba nadando en el río frío.
translation^: pepa was swimming in the cold river
pepa estaba nadando en el río frío.
translation^: pepa was swimming in the cold river
The answer should be "el río" the question is asking "Pepa was swimming in the cold ____" and "río" in English is river "Pepa was swimming in the cold river"