What kind of machine can generate negative ions indoors

A．near a pond with a water pump
B．close to a slow-flowing river
C．high in some barren mountains
D．by a rotating water sprinkler

A．watching animals to anticipate earthquakes is more effective than depending on seismographs
B．the unusual behavior of animals can not be trusted
C．neither watching nor using seismographs is reliable
D．earthquakes can not affect any animals