Those three countries are principal sources of Iran's trade.
A gaming tax and the sales tax are the principal sources of state income.
Commerce, agriculture, and livestock raising are the principal sources of income.
Eclipsing binaries are the principal sources of information on the masses and radii of stars.
A densely populated, fertile region, it constitutes one of the principal sources of Turkish tobacco.
Among these are hematite, magnetite, limonite, and siderite, which are the principal sources of iron; chalcopyrite, bornite, and chalcocite, the principal sources of copper; and sphalerite and galena, the principal sources, respectively, of zinc and lead.
Agriculture, livestock, and food processing are the principal sources of income, and there is some light manufacturing.
Hydroelectric power and coal are the principal sources of energy in Serbia, which has no nuclear power stations.
The principal sources of imports are the United States, Japan, Germany, Italy, the United Kingdom, and Taiwan.
His De artibus ac disciplinis liberalium litterarum contains one of the principal sources of early medieval music theory, Institutiones musicae.
Local medicinal springs account for some tourism, but the principal sources of income are agriculture, production of foodstuffs, and fishing.
