sources of economic sources of electrical sources of electricity sources of emissions sources of employment sources of energy sources of environmental sources of error sources of errors sources of evidence sources of exposure sources of external sources of federal sources of fiber sources of finance sources of financial sources of financing sources of food sources of foreign sources of funding sources of funds sources of greenhouse sources of growth sources of happiness sources of health sources of heat sources of help sources of human sources of ignition sources of income sources of infection sources of influence sources of information sources of innovation sources of inspiration sources of interference sources of international law sources of investment sources of iron sources of knowledge sources of law sources of lead sources of life sources of light sources of magnesium sources of mercury sources of methane sources of money sources of motivation sources of natural sources of new sources of news sources of nitrogen sources of noise sources of pollution sources of potassium sources of potential sources of power sources of protein sources of public sources of radiation sources of raw sources of renewable energy sources of resistance sources of revenue sources of revenues sources of risk sources of social sources of stress sources of sugar sources of supply sources of support sources of tension sources of traffic sources of uncertainty sources of value sources of variation sources of vitamin sources of vitamin d sources of vitamins sources of water sources of wealth sources of zinc sources on the internet sources online sources other sources present sources provide sources refer sources referred sources report sources reported sources reveal sources said sources say sources see sources should sources show sources state