The two words economists use most often are a. inflation and trade. b. supply and demand. c. competition and prices. d. markets and equilibrium.

supply and demand

Explanation: SUPPLY AND DEMAND are of great importance to an economist as this helps in determining and influence market price of goods and services. Supply refers to the number of goods and services that are available in the market place at a give time and at a particular market price while demand is quantity of goods consumer are willing and ready to buy at a particularr time and market price. A shift in demand or supply results in a change in price

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question - in 1827, john walker, a druggist in a small english town, tipped a splint with sulphur, chlorate of potash, and sulphid of antimony, and rubbed it on sandpaper, and it burst into flame. the druggist had discovered the first friction-chemical match, the kind we use to-day. it is called friction-chemical because it is made by mixing certain chemicals together and rubbing them. although walker's match did not require the bottle of acid, nevertheless it was not a good one. it could be lighted only by hard rubbing, and it sputtered and threw fire in all directions. in a few years, however, phosphorus was substituted on the tip for antimony, and the change worked wonders. the match could now be lighted with very little rubbing, and it was no longer necessary to have sandpaper upon which to rub it. it would ignite when rubbed on any dry surface, and there was no longer any sputtering. this was the phosphorus match, the match with which we are so familiar. according the paragraph what was the benefit of the new phosphorus match? it burst into flame when rubbed on sandpaper. it was made by mixing chemicals. it could be ignited on any dry surface. it threw fire in all directions.

answer - matches required natural chemicals