Trade involves the transfer of goods or services from one person or entity to another, often in exchange for money. A system or network that allows trade is called a market.
The product of mental labor — science — always stands far below its value, because the labor-time necessary to reproduce it has no relation at all to the labor-time required for its original production.
Karl Marx Addenda, "Relative and Absolute Surplus Value" in Economic Manuscripts (1861–63).
Protection and sustainable use of water supply is one of the most important environmental issues facing humanity. Groundwater is the primary source of drinking water for much of the world, as well as being vital for agriculture and industry, but it is under threat from pollution.
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