Completar frases completaVersión en línea completa los cambios de agua en el relieve de la tierra por FELIX GELDER 1 course course mouth course Source : the starting point of the river Upper : the initial stage of the river in the mountains . Middle : where the river flows more slowly through landscapes that are less steep . Lower : the river flows slowly and deposits the rocks . The : the water carried by the river flows into another river , a lake or the sea .