Which of the following best describes how historians use time periods? a. to classify origins of species b. to organize time since the earth began c. to break up time to make it easier to study d. to categorize human history according to social or political themes select the best answer from the choices provided a b c d

C

Explanation:

c. to break up time to make it easier to study" is the best example of how historians use time periods, although they are also used to separate cultural shifts.

you probably know the answer. stop asking stupid questions and making me waste my time. j.k. ; )   b.t.w. what are three ratios equivalent to 5 : 11? thx

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