The fall line was an important early source of water power.
Today they are an important source of food all over the world.
They are the most important source of energy for your body.
They used the river as an important source of food and a place for trade.
She is an important source of order in his life.
"Family members are the most important source of help for older people."
Also an important source of energy was water power at low or high pressure.
Fat is an important source of energy for the body.
The work is an important source of information about economic, social and cultural life in the 15th century.
The river has provided an important source of power in the past.
