upper trough lower trough coupling

at the eastern foot of Helan Mountain

Eastern foot of Helan Mountain

eastern foot of Helan Moutain

Helan County

Helan Mountain

Helan Mountain area

Helan Mountain Nature Reserve

Helan Mountains

Helan National Nature Reserve

Northern Helan Mountain

the Helan mountain

The Helan Mountains

acclivitous trough

across settlement trough

adjustable feeding trough

agitated trough dryer

air trough board

Alumina-magnesia tilting trough