Michael, aged four, loves playing with toy cars and airplanes, and his idea of play involves wrestling and pushing his friends. melanie, also aged four, loves playing with her dolls and doll house, and her idea of play is to have a tea party with her dolls and friends. both are exhibiting

sex-typed behavior

Explanation:

If sex-typed behavior are the ones which have the certain pursuits or attributes that are mostly considered to be as appropriate only for one of the sex/gender, i.e. sex-typed behavior are characterized to be mostly appropriate for only one of the sex or gender rather than being for the other one as well.

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